[▲ Vercel Community](/) · [Categories](/categories) · [Latest](/latest) · [Top](/top) · [Live](/live) [Help](/c/help/9) # Getting 500 Internal Server Error FastAPI 228 views · 0 likes · 3 posts Abanerjee Wsu (@abanerjee-wsu) · 2025-11-21 Hi all, I am developing a simple Agentic AI App using following Stack Nextjs --> Frontend FastAPI --> Backend Clerk - Authentication I am seeing 500 Internal Server error when its fastapi endpoint is being accessed by the frontend Currently receiving 500 error when accessing the fastapi endpoint on vercel. Expecting a success/200 response ``` **Build Logs** 00:06:06.286 Running build in Washington, D.C., USA (East) – iad1 00:06:06.287 Build machine configuration: 2 cores, 8 GB 00:06:06.422 Retrieving list of deployment files... 00:06:06.900 Downloading 28 deployment files... 00:06:07.675 Restored build cache from previous deployment (Aasp2edaCZy3FmQxfbpohHctPaA5) 00:06:08.196 Running "vercel build" 00:06:08.782 Vercel CLI 48.10.3 00:06:09.130 Installing dependencies... 00:06:10.433 00:06:10.433 up to date in 1s 00:06:10.434 00:06:10.434 229 packages are looking for funding 00:06:10.434 run `npm fund` for details 00:06:10.462 Detected Next.js version: 15.5.6 00:06:10.467 Running "npm run build" 00:06:10.653 00:06:10.653 > saas@0.1.0 build 00:06:10.654 > next build 00:06:10.654 00:06:11.792 ▲ Next.js 15.5.6 00:06:11.793 00:06:11.862 Linting and checking validity of types ... 00:06:17.067 Creating an optimized production build ... 00:06:21.553 ✓ Compiled successfully in 1960ms 00:06:21.555 Collecting page data ... 00:06:22.930 Generating static pages (0/5) ... 00:06:23.820 Generating static pages (1/5) 00:06:23.821 Generating static pages (2/5) 00:06:23.821 Generating static pages (3/5) 00:06:23.821 ✓ Generating static pages (5/5) 00:06:24.282 Finalizing page optimization ... 00:06:24.285 Collecting build traces ... 00:06:32.012 00:06:32.015 Route (pages) Size First Load JS 00:06:32.015 ┌ ○ / (549 ms) 3.08 kB 146 kB 00:06:32.016 ├ /_app 0 B 142 kB 00:06:32.016 ├ ○ /404 180 B 143 kB 00:06:32.016 ├ ○ /product (547 ms) 45.4 kB 188 kB 00:06:32.016 └ ○ /sign-in/[[...index]] (546 ms) 1.51 kB 144 kB 00:06:32.016 + First Load JS shared by all 147 kB 00:06:32.016 ├ chunks/framework-acd67e14855de5a2.js 57.7 kB 00:06:32.016 ├ chunks/main-62a5bcb5d940e2e2.js 36.8 kB 00:06:32.016 ├ chunks/pages/_app-36c145dffa6388ad.js 46.3 kB 00:06:32.016 └ other shared chunks (total) 5.86 kB 00:06:32.017 00:06:32.017 ○ (Static) prerendered as static content 00:06:32.017 00:06:32.069 Collected static files (public/, static/, .next/static): 3.923ms 00:06:33.753 Using Python 3.12 from pyproject.toml 00:06:35.062 Installing required dependencies from uv.lock... 00:06:35.063 Using uv at "/usr/local/bin/uv" 00:06:36.434 Build Completed in /vercel/output [27s] 00:06:36.662 Deploying outputs... 00:06:46.177 Deployment completed 00:06:46.834 Creating build cache... 00:07:00.688 Created build cache: 13.855s 00:07:00.690 Uploading build cache [170.82 MB] 00:07:02.773 Build cache uploaded: 2.083s ``` **Runtime logs** `Python process exited with exit status: 1. The logs above can help with debugging the issue.` **api/index.py code** ``` import os from fastapi import FastAPI, Depends from fastapi.responses import StreamingResponse from fastapi.middleware.cors import CORSMiddleware from fastapi_clerk_auth import ClerkConfig, ClerkHTTPBearer, HTTPAuthorizationCredentials from openai import OpenAI print("[DEBUG] Starting api/index.py import...") app = FastAPI() # Add CORS middleware app.add_middleware( CORSMiddleware, allow_origins=["*"], allow_credentials=True, allow_methods=["*"], allow_headers=["*"], ) print("[DEBUG] FastAPI app and CORS configured") # Configure Clerk authentication clerk_config = ClerkConfig(jwks_url=os.getenv("CLERK_JWKS_URL")) clerk_guard = ClerkHTTPBearer(clerk_config) print(f"[DEBUG] Clerk configured with JWKS URL: {os.getenv('CLERK_JWKS_URL')}") print(f"[DEBUG] OpenAI API key present: {bool(os.getenv('OPENAI_API_KEY'))}") @app.get("/api/health") @app.get("/health") async def health_check(): """Health check endpoint that doesn't require authentication""" return {"status": "healthy", "service": "api"} @app.get("/api/idea") @app.get("/idea") def generate_idea(creds: HTTPAuthorizationCredentials = Depends(clerk_guard)): """ Generate a business idea using OpenAI GPT-4o-mini with streaming response. Requires Clerk authentication via Authorization header. """ user_id = creds.decoded["sub"] # User ID from JWT print(f"[INFO] Generating idea for user: {user_id}") client = OpenAI(api_key=os.getenv("OPENAI_API_KEY")) prompt = [ { "role": "user", "content": "Reply with a new business idea for AI Agents, formatted with headings, sub-headings and bullet points" } ] stream = client.chat.completions.create( model="gpt-4o-mini", messages=prompt, max_tokens=500, temperature=0.7, stream=True ) def event_stream(): try: for chunk in stream: if chunk.choices[0].delta.content is not None: text = chunk.choices[0].delta.content # Escape newlines for SSE format safe_text = text.replace('\n', '\\n') yield f"data: {safe_text}\n\n" yield "data: [DONE]\n\n" except Exception as e: print(f"[ERROR] Stream error: {e}") yield f"data: [ERROR] {str(e)}\n\n" return StreamingResponse( event_stream(), media_type="text/event-stream", headers={ "Cache-Control": "no-cache", "X-Accel-Buffering": "no" } ) @app.get("/api/user") @app.get("/user") def get_user_info(creds: HTTPAuthorizationCredentials = Depends(clerk_guard)): """Get information about the authenticated user.""" return { "user_id": creds.decoded.get("sub"), "email": creds.decoded.get("email"), "claims": creds.decoded } # Vercel serverless function handler handler = app print("[DEBUG] Module initialization complete") ``` **Current project structure** <!-- Project information (URL, framework, environment, project settings) --> **Project structure** ``` aas/ ├── .env.local ├── .gitignore ├── README.md ├── eslint.config.mjs ├── next-env.d.ts ├── next.config.ts ├── package-lock.json ├── package.json ├── postcss.config.mjs ├── pyproject.toml ├── requirements.txt ├── run-api.sh ├── runtime.txt ├── tsconfig.json ├── tsconfig.tsbuildinfo ├── uv.lock ├── vercel.json │ ├── api/ │ ├── __pycache__/ │ │ └── index.cpython-314.pyc │ └── index.py │ ├── pages/ │ ├── _app.tsx │ ├── index.tsx │ ├── product.tsx │ │ │ ├── api/ │ │ └── _debug/ │ │ │ └── sign-in/ │ └── [[...index]].tsx │ ├── public/ │ ├── favicon.ico │ ├── file.svg │ ├── globe.svg │ ├── next.svg │ ├── vercel.svg │ └── window.svg │ └── styles/ └── globals.css ``` system (@system) · 2025-11-21 There's another community post with 404 debugging tips that might be helpful. Please give these solutions a try and let us know how it goes. https://community.vercel.com/t/debugging-404-errors/437 A human should be around soon to offer more advice. But you can also get helpful information quickly by asking [v0](https://v0.dev/). fmoor (@fmoor) · 2025-12-05 I tried using the python source you posted and it seems that the handler variable might be the problem here. If you are using a WSGI or ASGI framework like fastapi then you don’t want the handler variable. Vercel interprets handler as a BaseHTTPRequestHandler value. There is a runtime check that asserts that hander is a subclass of BaseHTTPRequestHandler. If this check fails then the API call fails with status 500. The relevant blerb in the docs is [here](https://vercel.com/docs/functions/runtimes/python#other-python-frameworks).