Tuần trước, một khách hàng của tôi gặp cảnh tượng như thế này: CTO gọi điện lúc 11 giờ đêm hỏi "Tại sao chi phí API tháng này tăng 340%?" và đội kỹ thuật không có câu trả lời. Không ai biết user nào đang burn tiền, model nào gây ra bottleneck, hay project nào có request bất thường. Đó là lúc tôi nhận ra chargeback attribution không phải là luxury — mà là survival.

Trong bài viết này, tôi sẽ chia sẻ cách xây dựng hệ thống phân bổ chi phí API AI hoàn chỉnh bằng HolySheep AI, với chi phí thực tế và code có thể chạy ngay hôm nay.

Tại Sao Chargeback Attribution Quan Trọng?

Khi team phát triển AI features mà không tracking chi phí, bạn sẽ gặp 3 vấn đề cổ điển:

Với HolySheep AI, bạn có dashboard native phân bổ chi phí theo user/project/model/request-type ngay trong console. Kết hợp với API call logging tự động, bạn sẽ có báo cáo internal settlement chính xác đến cent.

Kiến Trúc Hệ Thống Chargeback

Tôi thiết kế hệ thống gồm 3 layers:

Code Implementation

1. Wrapper Client Với Metadata Auto-Tagging

Đây là code tôi dùng thực tế cho 5 dự án production. Wrapper này tự động attach user_id, project_id và request_type vào mỗi API call:

"""
HolySheep AI API Client với Auto-Tagging cho Chargeback
Author: HolySheep AI Team
"""

import requests
import time
import hashlib
from datetime import datetime, timezone
from typing import Optional, Dict, Any, List
from dataclasses import dataclass, asdict
import json

@dataclass
class RequestMetadata:
    user_id: str
    project_id: str
    request_type: str  # 'chat', 'embedding', 'vision', 'moderation'
    model_override: Optional[str] = None

class HolySheepChargebackClient:
    """Client với built-in chargeback tracking"""
    
    BASE_URL = "https://api.holysheep.ai/v1"
    
    def __init__(self, api_key: str):
        self.api_key = api_key
        self.session = requests.Session()
        self.session.headers.update({
            "Authorization": f"Bearer {api_key}",
            "Content-Type": "application/json"
        })
        # In-memory cache cho demo; production dùng Redis
        self._request_log: List[Dict] = []
        self._start_time = time.time()
    
    def _generate_request_id(self, metadata: RequestMetadata) -> str:
        """Tạo unique request ID cho tracking"""
        timestamp = datetime.now(timezone.utc).isoformat()
        raw = f"{metadata.user_id}:{metadata.project_id}:{timestamp}"
        return hashlib.sha256(raw.encode()).hexdigest()[:16]
    
    def _estimate_cost(self, model: str, input_tokens: int, 
                       output_tokens: int) -> float:
        """Tính chi phí dựa trên model pricing (2026 rates)"""
        pricing = {
            # GPT-4.1 family
            "gpt-4.1": {"input": 8.0, "output": 32.0},  # $8/$32 per MTok
            "gpt-4.1-mini": {"input": 1.0, "output": 4.0},
            "gpt-4.1-nano": {"input": 0.25, "output": 1.0},
            # Claude family
            "claude-sonnet-4.5": {"input": 15.0, "output": 75.0},
            "claude-opus-4": {"input": 75.0, "output": 150.0},
            "claude-haiku-3.5": {"input": 1.5, "output": 6.0},
            # Gemini family
            "gemini-2.5-flash": {"input": 2.50, "output": 10.0},
            "gemini-2.5-pro": {"input": 15.0, "output": 60.0},
            # DeepSeek family
            "deepseek-v3.2": {"input": 0.42, "output": 1.68},
            "deepseek-r1": {"input": 0.55, "output": 2.20},
        }
        
        rates = pricing.get(model, {"input": 5.0, "output": 20.0})
        input_cost = (input_tokens / 1_000_000) * rates["input"]
        output_cost = (output_tokens / 1_000_000) * rates["output"]
        return round(input_cost + output_cost, 6)
    
    def chat_completion(self, messages: List[Dict], metadata: RequestMetadata,
                        model: str = "gpt-4.1-mini", 
                        **kwargs) -> Dict[str, Any]:
        """Gọi chat completion với auto-cost tracking"""
        request_id = self._generate_request_id(metadata)
        start_ts = time.time()
        
        try:
            response = self.session.post(
                f"{self.BASE_URL}/chat/completions",
                json={
                    "model": metadata.model_override or model,
                    "messages": messages,
                    **kwargs
                },
                timeout=30
            )
            latency_ms = round((time.time() - start_ts) * 1000, 2)
            
            # Parse response để lấy token usage
            result = response.json()
            usage = result.get("usage", {})
            input_tokens = usage.get("prompt_tokens", 0)
            output_tokens = usage.get("completion_tokens", 0)
            estimated_cost = self._estimate_cost(
                result.get("model", model), 
                input_tokens, 
                output_tokens
            )
            
            # Log cho chargeback report
            log_entry = {
                "request_id": request_id,
                "timestamp": datetime.now(timezone.utc).isoformat(),
                "user_id": metadata.user_id,
                "project_id": metadata.project_id,
                "request_type": metadata.request_type,
                "model": result.get("model", model),
                "input_tokens": input_tokens,
                "output_tokens": output_tokens,
                "latency_ms": latency_ms,
                "estimated_cost_usd": estimated_cost,
                "status": "success"
            }
            self._request_log.append(log_entry)
            
            # Attach metadata vào response
            result["_chargeback"] = log_entry
            return result
            
        except requests.exceptions.Timeout as e:
            log_entry = {
                "request_id": request_id,
                "timestamp": datetime.now(timezone.utc).isoformat(),
                "user_id": metadata.user_id,
                "project_id": metadata.project_id,
                "request_type": metadata.request_type,
                "model": model,
                "error": "TimeoutError",
                "latency_ms": round((time.time() - start_ts) * 1000, 2),
                "status": "failed"
            }
            self._request_log.append(log_entry)
            raise TimeoutError(f"Request timeout sau 30s: {e}")
            
        except requests.exceptions.HTTPError as e:
            log_entry = {
                "request_id": request_id,
                "timestamp": datetime.now(timezone.utc).isoformat(),
                "user_id": metadata.user_id,
                "project_id": metadata.project_id,
                "request_type": metadata.request_type,
                "model": model,
                "error": f"HTTP_{e.response.status_code}",
                "status": "failed"
            }
            self._request_log.append(log_entry)
            raise
    
    def get_chargeback_report(self, 
                              group_by: str = "user_id") -> Dict[str, Any]:
        """Generate chargeback report theo user/project/model/request_type"""
        if not self._request_log:
            return {"error": "Không có request logs"}
        
        successful_logs = [l for l in self._request_log if l["status"] == "success"]
        
        if group_by == "user_id":
            groups = {}
            for log in successful_logs:
                user = log["user_id"]
                if user not in groups:
                    groups[user] = {
                        "total_requests": 0,
                        "total_input_tokens": 0,
                        "total_output_tokens": 0,
                        "total_cost_usd": 0.0,
                        "avg_latency_ms": 0.0,
                        "by_project": {},
                        "by_model": {}
                    }
                groups[user]["total_requests"] += 1
                groups[user]["total_input_tokens"] += log["input_tokens"]
                groups[user]["total_output_tokens"] += log["output_tokens"]
                groups[user]["total_cost_usd"] += log["estimated_cost_usd"]
                
                # Breakdown by project
                proj = log["project_id"]
                if proj not in groups[user]["by_project"]:
                    groups[user]["by_project"][proj] = {"cost": 0.0, "requests": 0}
                groups[user]["by_project"][proj]["cost"] += log["estimated_cost_usd"]
                groups[user]["by_project"][proj]["requests"] += 1
                
                # Breakdown by model
                model = log["model"]
                if model not in groups[user]["by_model"]:
                    groups[user]["by_model"][model] = {"cost": 0.0, "requests": 0}
                groups[user]["by_model"][model]["cost"] += log["estimated_cost_usd"]
                groups[user]["by_model"][model]["requests"] += 1
            
            # Calculate averages
            for user in groups:
                count = groups[user]["total_requests"]
                total_latency = sum(
                    l["latency_ms"] for l in successful_logs 
                    if l["user_id"] == user
                )
                groups[user]["avg_latency_ms"] = round(total_latency / count, 2)
                groups[user]["total_cost_usd"] = round(groups[user]["total_cost_usd"], 6)
            
            return groups
        
        return {"error": f"Unsupported group_by: {group_by}"}

============ DEMO USAGE ============

if __name__ == "__main__": # Khởi tạo client với API key của bạn client = HolySheepChargebackClient("YOUR_HOLYSHEEP_API_KEY") # Simulate requests từ different users/projects metadata_user_a = RequestMetadata( user_id="[email protected]", project_id="project_marketing_automation", request_type="chat" ) # Mock call - trong production sẽ gọi thật print("Demo chargeback tracking:") print(f"Client initialized: {client.BASE_URL}") print(f"Pricing loaded for 12+ models") print("\nSẵn sàng track requests!")

2. PostgreSQL Schema Cho Production Scale

Với hệ thống production handle 100K+ requests/ngày, tôi recommend dùng PostgreSQL với TimescaleDB extension cho time-series optimization:

-- HolySheep Chargeback Database Schema
-- Chạy trên PostgreSQL 15+ với TimescaleDB extension

-- Enable TimescaleDB
CREATE EXTENSION IF NOT EXISTS timescaledb CASCADE;

-- Main request logs table
CREATE TABLE api_request_logs (
    id BIGSERIAL PRIMARY KEY,
    request_id VARCHAR(16) NOT NULL UNIQUE,
    user_id VARCHAR(255) NOT NULL,
    project_id VARCHAR(255) NOT NULL,
    request_type VARCHAR(50) NOT NULL, -- chat, embedding, vision, moderation
    model VARCHAR(100) NOT NULL,
    input_tokens INTEGER NOT NULL DEFAULT 0,
    output_tokens INTEGER NOT NULL DEFAULT 0,
    latency_ms DECIMAL(10, 2) NOT NULL,
    estimated_cost_usd DECIMAL(12, 6) NOT NULL,
    status VARCHAR(20) NOT NULL, -- success, failed, timeout
    error_message TEXT,
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

-- Convert to hypertable (TimescaleDB)
SELECT create_hypertable('api_request_logs', 'created_at', 
    chunk_time_interval => INTERVAL '1 day');

-- Indexes cho fast querying
CREATE INDEX idx_logs_user_id ON api_request_logs (user_id);
CREATE INDEX idx_logs_project_id ON api_request_logs (project_id);
CREATE INDEX idx_logs_model ON api_request_logs (model);
CREATE INDEX idx_logs_request_type ON api_request_logs (request_type);
CREATE INDEX idx_logs_created_at ON api_request_logs (created_at DESC);

-- Continuous Aggregate cho hourly reports (pre-computed)
CREATE MATERIALIZED VIEW hourly_cost_by_user
WITH (timescaledb.continuous) AS
SELECT 
    time_bucket('1 hour', created_at) AS hour,
    user_id,
    project_id,
    model,
    COUNT(*) AS total_requests,
    SUM(input_tokens) AS total_input_tokens,
    SUM(output_tokens) AS total_output_tokens,
    SUM(estimated_cost_usd) AS total_cost_usd,
    AVG(latency_ms) AS avg_latency_ms
FROM api_request_logs
WHERE status = 'success'
GROUP BY 1, 2, 3, 4;

-- Continuous Aggregate cho daily reports
CREATE MATERIALIZED VIEW daily_cost_summary
WITH (timescaledb.continuous) AS
SELECT 
    time_bucket('1 day', created_at) AS day,
    user_id,
    project_id,
    request_type,
    model,
    COUNT(*) AS total_requests,
    SUM(input_tokens) AS total_input_tokens,
    SUM(output_tokens) AS total_output_tokens,
    SUM(estimated_cost_usd) AS total_cost_usd
FROM api_request_logs
WHERE status = 'success'
GROUP BY 1, 2, 3, 4, 5;

-- Function để generate chargeback report
CREATE OR REPLACE FUNCTION generate_chargeback_report(
    p_start_date TIMESTAMPTZ,
    p_end_date TIMESTAMPTZ,
    p_group_by VARCHAR(50) DEFAULT 'user_id'
)
RETURNS TABLE (
    group_key VARCHAR(255),
    total_requests BIGINT,
    total_input_tokens BIGINT,
    total_output_tokens BIGINT,
    total_cost_usd DECIMAL(14, 6),
    avg_latency_ms DECIMAL(10, 2),
    top_model VARCHAR(100),
    top_model_cost DECIMAL(14, 6)
) AS $$
BEGIN
    IF p_group_by = 'user_id' THEN
        RETURN QUERY
        SELECT 
            l.user_id,
            COUNT(*)::BIGINT,
            SUM(l.input_tokens)::BIGINT,
            SUM(l.output_tokens)::BIGINT,
            SUM(l.estimated_cost_usd),
            AVG(l.latency_ms),
            mode() WITHIN GROUP (ORDER BY l.model)::VARCHAR(100),
            MAX(subq.model_cost)::DECIMAL(14, 6)
        FROM api_request_logs l
        LEFT JOIN LATERAL (
            SELECT model, SUM(estimated_cost_usd) as model_cost
            FROM api_request_logs l2
            WHERE l2.user_id = l.user_id
                AND l2.created_at BETWEEN p_start_date AND p_end_date
            GROUP BY model
            ORDER BY model_cost DESC
            LIMIT 1
        ) subq ON TRUE
        WHERE l.status = 'success'
            AND l.created_at BETWEEN p_start_date AND p_end_date
        GROUP BY l.user_id
        ORDER BY SUM(l.estimated_cost_usd) DESC;
        
    ELSIF p_group_by = 'project_id' THEN
        RETURN QUERY
        SELECT 
            l.project_id,
            COUNT(*)::BIGINT,
            SUM(l.input_tokens)::BIGINT,
            SUM(l.output_tokens)::BIGINT,
            SUM(l.estimated_cost_usd),
            AVG(l.latency_ms),
            mode() WITHIN GROUP (ORDER BY l.model)::VARCHAR(100),
            MAX(subq.model_cost)::DECIMAL(14, 6)
        FROM api_request_logs l
        LEFT JOIN LATERAL (
            SELECT model, SUM(estimated_cost_usd) as model_cost
            FROM api_request_logs l2
            WHERE l2.project_id = l.project_id
                AND l2.created_at BETWEEN p_start_date AND p_end_date
            GROUP BY model
            ORDER BY model_cost DESC
            LIMIT 1
        ) subq ON TRUE
        WHERE l.status = 'success'
            AND l.created_at BETWEEN p_start_date AND p_end_date
        GROUP BY l.project_id
        ORDER BY SUM(l.estimated_cost_usd) DESC;
    END IF;
END;
$$ LANGUAGE plpgsql;

-- Refresh materialized views
SELECT add_continuous_aggregate_policy('hourly_cost_by_user',
    start_offset => INTERVAL '3 hours',
    end_offset => INTERVAL '1 hour',
    schedule_interval => INTERVAL '1 hour');

SELECT add_continuous_aggregate_policy('daily_cost_summary',
    start_offset => INTERVAL '1 day',
    end_offset => INTERVAL '1 hour',
    schedule_interval => INTERVAL '1 hour');

-- Sample queries
-- 1. Top 10 users by cost trong 7 ngày
SELECT * FROM generate_chargeback_report(
    NOW() - INTERVAL '7 days',
    NOW(),
    'user_id'
) LIMIT 10;

-- 2. Cost by project trong tháng
SELECT * FROM generate_chargeback_report(
    DATE_TRUNC('month', NOW()),
    NOW(),
    'project_id'
);

3. Integration Với HolySheep API Dashboard

#!/bin/bash

HolySheep AI - Export chargeback data cho internal billing system

Chạy via cron: 0 6 * * * /opt/scripts/holyheep-chargeback-export.sh

HOLYSHEEP_API_KEY="YOUR_HOLYSHEEP_API_KEY" HOLYSHEEP_API_BASE="https://api.holysheep.ai/v1" OUTPUT_DIR="/var/chargeback/exports" DATE=$(date +%Y-%m-%d) TIMESTAMP=$(date +%Y%m%d_%H%M%S)

Tạo output directory nếu chưa có

mkdir -p ${OUTPUT_DIR} echo "=== HolySheep AI Chargeback Export ===" echo "Timestamp: $(date)" echo ""

1. Export usage summary qua HolySheep Dashboard API

echo "[1/4] Fetching usage summary..." curl -s -X GET "${HOLYSHEEP_API_BASE}/dashboard/usage" \ -H "Authorization: Bearer ${HOLYSHEEP_API_KEY}" \ -H "Content-Type: application/json" \ | jq '.data' > ${OUTPUT_DIR}/usage_summary_${DATE}.json if [ $? -eq 0 ]; then echo "✓ Usage summary saved" else echo "✗ Failed to fetch usage summary" fi

2. Export cost breakdown by model

echo "[2/4] Fetching cost by model..." curl -s -X GET "${HOLYSHEEP_API_BASE}/dashboard/costs?group_by=model" \ -H "Authorization: Bearer ${HOLYSHEEP_API_KEY}" \ -H "Content-Type: application/json" \ | jq '.breakdown' > ${OUTPUT_DIR}/cost_by_model_${DATE}.json

3. Export cost breakdown by project (nếu có project tagging)

echo "[3/4] Fetching cost by project..." curl -s -X GET "${HOLYSHEEP_API_BASE}/dashboard/costs?group_by=project" \ -H "Authorization: Bearer ${HOLYSHEEP_API_KEY}" \ -H "Content-Type: application/json" \ | jq '.breakdown' > ${OUTPUT_DIR}/cost_by_project_${DATE}.json 2>/dev/null

4. Generate CSV report cho Finance team

echo "[4/4] Generating CSV report..." cat > ${OUTPUT_DIR}/chargeback_report_${TIMESTAMP}.csv << 'EOF' user_id,project_id,model,request_type,total_requests,total_input_tokens,total_output_tokens,total_cost_usd,avg_latency_ms EOF

Merge JSON exports vào CSV (sample format)

jq -r '.users[] | [.user_id, .project_id, .model, .type, .count, .input_tokens, .output_tokens, .cost, .avg_latency] | @csv' \ ${OUTPUT_DIR}/usage_summary_${DATE}.json >> ${OUTPUT_DIR}/chargeback_report_${TIMESTAMP}.csv

Upload lên S3/GCS cho long-term storage

echo "" echo "Uploading to storage..." aws s3 cp ${OUTPUT_DIR}/chargeback_report_${TIMESTAMP}.csv \ s3://your-bucket/chargeback/$(date +%Y)/${DATE}/ 2>/dev/null || \ gsutil cp ${OUTPUT_DIR}/chargeback_report_${TIMESTAMP}.csv \ gs://your-bucket/chargeback/$(date +%Y)/${DATE}/ 2>/dev/null || \ echo "(S3/GCS upload skipped - configure credentials)"

Cleanup files older than 90 days

find ${OUTPUT_DIR} -type f -mtime +90 -delete echo "" echo "✓ Export completed: ${OUTPUT_DIR}/chargeback_report_${TIMESTAMP}.csv"

Bảng So Sánh Chi Phí: HolySheep vs Official APIs

Model HolySheep ($/MTok In) Official ($/MTok In) Tiết kiệm Latency P50 Use Case
GPT-4.1 $8.00 $15.00 47% <50ms Complex reasoning, code generation
Claude Sonnet 4.5 $15.00 $30.00 50% <45ms Long-form writing, analysis
Gemini 2.5 Flash $2.50 $7.50 67% <30ms High-volume, real-time apps
DeepSeek V3.2 $0.42 $2.80 85% <40ms Cost-sensitive production workloads
DeepSeek R1 $0.55 $3.70 85% <60ms Advanced reasoning tasks

Phù hợp / Không phù hợp với ai

✅ Nên dùng HolySheep chargeback system nếu bạn:

❌ Có thể không cần thiết nếu:

Giá và ROI

Plan Giá/tháng API Credits Tính năng ROI vs Official
Free $0 $5 credits Basic API, dashboard Thử nghiệm
Starter $49 $500 credits + Project tagging, exports Tiết kiệm 40-60%
Pro $199 $2,500 credits + Team seats, audit logs Tiết kiệm 50-70%
Enterprise Custom Unlimited + SSO, SLA 99.9%, Dedicated support Tiết kiệm 60-85%

Example ROI calculation: Team 10 người, mỗi người dùng $200 API tháng. Với HolySheep, cùng usage chỉ tốn ~$80-100/tháng. Tiết kiệm $1,000-1,200/năm = 1 chiếc MacBook Air.

Vì sao chọn HolySheep cho Chargeback

Qua 2 năm triển khai AI systems cho các startup và enterprise, tôi đã thử qua OpenAI, Anthropic, Azure AI trực tiếp. Lý do tôi chọn HolySheep AI cho hệ thống chargeback:

Lỗi thường gặp và cách khắc phục

1. Lỗi "401 Unauthorized" - Invalid API Key

# Vấn đề:

requests.exceptions.HTTPError: 401 Client Error: Unauthorized

Nguyên nhân thường gặp:

1. API key chưa được set đúng format

2. Key đã bị revoke hoặc hết hạn

3. Dùng key của environment khác (test vs production)

Cách khắc phục:

1. Kiểm tra format key (phải bắt đầu bằng "hs_" hoặc "sk-")

YOUR_HOLYSHEEP_API_KEY = "hs_xxxxxxxxxxxx" # KHÔNG phải sk-xxxx

2. Verify key còn active

curl -X GET "https://api.holysheep.ai/v1/models" \ -H "Authorization: Bearer ${YOUR_HOLYSHEEP_API_KEY}"

3. Nếu key hết hạn, tạo key mới tại:

https://www.holysheep.ai/dashboard/api-keys

4. Verify environment variable

import os api_key = os.environ.get('HOLYSHEEP_API_KEY') if not api_key or len(api_key) < 20: raise ValueError("Invalid API key format")

2. Lỗi "ConnectionError: timeout" - Request Timeout

# Vấn đề:

requests.exceptions.ConnectTimeout: Connection timed out

Nguyên nhân:

1. Network firewall chặn port 443

2. Proxy/Corporate VPN blocking

3. DNS resolution fail

4. Server overloaded (503)

Cách khắc phục:

1. Kiểm tra connectivity

import socket try: socket.create_connection(("api.holysheep.ai", 443), timeout=5) print("✓ Connectivity OK") except OSError as e: print(f"✗ Network error: {e}")

2. Thêm retry logic với exponential backoff

import time from requests.adapters import HTTPAdapter from urllib3.util.retry import Retry def create_session_with_retry(): session = requests.Session() retry_strategy = Retry( total=3, backoff_factor=1, status_forcelist=[429, 500, 502, 503, 504], ) adapter = HTTPAdapter(max_retries=retry_strategy) session.mount("https://", adapter) session.mount("http://", adapter) return session

3. Tăng timeout cho requests lớn

response = session.post( f"{HOLYSHEEP_BASE}/chat/completions", json=payload, timeout=(10, 60) # (connect_timeout, read_timeout) )

4. Kiểm tra proxy settings

os.environ['NO_PROXY'] = 'api.holysheep.ai' os.environ['HTTPS_PROXY'] = '' # Xóa proxy nếu đang dùng

3. Lỗi "400 Bad Request" - Invalid Payload Format

# Vấn đề:

requests.exceptions.HTTPError: 400 Client Error: Bad Request

Nguyên nhân:

1. Invalid JSON structure

2. Missing required fields

3. Model name không tồn tại

4. Token limit exceeded

Cách khắc phục:

1. Validate payload structure trước khi gửi

def validate_chat_payload(messages: List[Dict], model: str) -> bool: if not messages or len(messages) == 0: raise ValueError("messages không được rỗng") for msg in messages: if "role" not in msg or "content" not in msg: raise ValueError(f"Message thiếu required fields: {msg}") if msg["role"] not in ["system", "user", "assistant"]: raise ValueError(f"Invalid role: {msg['role']}") # Validate model name valid_models = [ "gpt-4.1", "gpt-4.1-mini", "gpt-4.1-nano", "claude-sonnet-4.5", "claude-opus-4", "claude-haiku-3.5", "gemini-2.5-flash", "gemini-2.5-pro", "deepseek-v3.2", "deepseek-r1" ] if model not in valid_models: raise ValueError(f"Model không hỗ trợ: {model}. Valid: {valid_models}") return True

2. Parse error response để debug

def handle_bad_request(response): try: error_detail = response.json() print(f"Error code: {error_detail.get('error', {}).get('code')}") print(f"Message: {error_detail.get('error', {}).get('message')}") except: print(f"Raw response: {response.text}") # Log để track pattern logger.error(f"400 Bad Request: {response.text}")

3. Example correct payload

payload = { "model": "gpt-4.1-mini", # Không phải "gpt-4" hay "gpt4" "messages": [ {"role": "system", "content": "Bạn là trợ lý hữu ích."}, {"role": "user",