Flask + NextJs works locally but Flask api do not work on Vercel

Link to the code that reproduces this issue

https://github.com/arnaud0617/nextjs-boilerplate

To Reproduce

I deployed the NexJS-boilerplate on vercel : it works
I added flask and it works locally http://localhost:3000/api/hello > return the right message "Hello! This is Arnaud, from Flask"
I uploaded in Vercel and get the error "https://****-projects.vercel.app/" is still working "https://***-projects.vercel.app/api/hello" is not working

I get the following error 404: NOT_FOUND Code: DNS_HOSTNAME_RESOLVED_PRIVATE ID: sfo1::n8s7h-1717543156736-e703ce3d0392

index.py from flask import Flask app = Flask(name)

@app.route('/api/hello', methods=['GET']) def hello_world(): return "Hello! This is Arnaud, from Flask"

if name == 'main': app.run(debug=True, port=5328)

next.config.js module.exports = { async rewrites() { return [ { source: '/api/:path', destination: 'http://localhost:5328/api/:path', // Proxy to Backend }, ] }, }

requirements.txt Flask==3.0.3

Current vs. Expected behavior

I deployed the NexJS-boilerplate on vercel : it works
I added flask and it works locally http://localhost:3000/api/hello > return the right message "Hello! This is Arnaud, from Flask"
I uploaded in Vercel and I does not work. I get the error 404: NOT_FOUND Code: DNS_HOSTNAME_RESOLVED_PRIVATE ID: sfo1::n8s7h-1717543156736-e703ce3d0392

index.py from flask import Flask app = Flask(name)

@app.route('/api/hello', methods=['GET']) def hello_world(): return "Hello! This is Arnaud, from Flask"

if name == 'main': app.run(debug=True, port=5328)

next.config.js module.exports = { async rewrites() { return [ { source: '/api/:path', destination: 'http://localhost:5328/api/:path', // Proxy to Backend }, ] }, }

requirements.txt Flask==3.0.3

Provide environment information

npx --no-install next info

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 16245
  Available CPU cores: 8
Binaries:
  Node: 20.13.1
  npm: N/A
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 14.2.3 // Latest available version is detected (14.2.3).
  eslint-config-next: 14.2.3
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.4.5
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Not sure, create-next-app, Script (next/script)

Which stage(s) are affected? (Select all that apply)

Vercel (Deployed)

Additional context

No response

vercel / next.js