Cannot install pip requirements

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1

Hello guys.
I have a project. It use Python Flask, a HTML builder(.md to .html). All of them are packages.
It is the requirements.txt:

Flask
HomepageBuilder/.
microsoft

The package microsoft is used to test install requirements. I don’t need the package.
The HomepageBuilder/. is not a pypi project.

vercel.json:

{
  "version": 2,
  "installCommand": "pip install -r requirements.txt",
  "buildCommand": "pip install -r requirements.txt",
  "builds": [
    {
      "src": "app.py",
      "use": "@vercel/python",
      "config": {
        "includeFiles": ["requirements.txt"]
      }
    }
  ],
  "routes": [
    {
      "src": "/(.*)",
      "dest": "app.py"
    }
  ]
}

When Vercel try to install requirements.txt, the console:

[21:54:34.303] Running build in Washington, D.C., USA (East) – iad1
[21:54:34.304] Build machine configuration: 2 cores, 8 GB
[21:54:34.322] Cloning github.com/***/*** (Branch: test, Commit: 5339c8e)
[21:54:34.773] Cloning completed: 451.000ms
[21:54:34.887] Restored build cache from previous deployment (DmDWn3SJZuS5M2Kxz2dceqjzdEVG)
[21:54:36.583] Running "vercel build"
[21:54:37.506] Vercel CLI 44.5.0
[21:54:37.684] WARN! Due to `builds` existing in your configuration file, the Build and Development Settings defined in your Project Settings will not apply. Learn More: https://vercel.link/unused-build-settings
[21:54:37.708] Installing required dependencies...
[21:54:47.542] Build Completed in /vercel/output [10s]
[21:54:47.659] Deploying outputs...
[21:54:55.380] 
[21:54:55.512] Deployment completed
[21:54:56.374] Uploading build cache [4.00 kB]...
[21:54:56.447] Build cache uploaded: 77.086ms

The package HomepageBuilder we can use builder to build some markdown documents.

And then the app.py excuted the command but it sh: line 1: builder: command not found.

Please help me, thank you!