[Python] Upload File operation using FastAPI does not work on Deta Cloud Platform

When I run this code via uvicorn main:app everything works, but when I run it using Deta, I get Internal Server Error and only GET endpoint works (the POST one is not even called as it was supposed to). Can you please help me? Thanks in advance.

import os
from pathlib import Path

from fastapi import FastAPI, Form, UploadFile
from fastapi.responses import FileResponse, HTMLResponse

from pdfpad import pdfpad, save_pdf


app = FastAPI()


@app.post("/processfile/")
async def process_file(file: UploadFile) -> FileResponse:
path = file.filename
if os.getenv("DETA_RUNTIME") == "true":
path = Path("/tmp") / file.filename
saved_path = save_pdf(pdfpad(await file.read()), path)
return FileResponse(saved_path)


@app.get("/")
async def main():
content = """
<body>
<form action="/processfile/" enctype="multipart/form-data" method="post" id="form1">

<label for file>Choose PDF:</label>
file: <input name="file" type="file" form="form1">
<br><br>

<input type="submit">
</form>
</body>
"""
return HTMLResponse(content=content)

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