Permission denied on App Platform with Python FastAPI

I have deployed a FastAPI application in Digitalocen App Platform and I’m trying to upload, write, and modify a file. This is the code I’m using:

@router.post(
    "/",
    response_model=schemas.GeneralResponseObj,
    status_code=status.HTTP_201_CREATED
)
async def load_file(file: UploadFile = File(...), source: str = ''):
    """
    Load a file
    """
    content = file.file.read()
    with open(file.filename, "wb") as f:
        f.write(content)
    # SOME CODE THAT READS THE FILE
    os.remove(file.filename)
    return schemas.GeneralResponseObj(
        message="Saved new data"
    )

It works locally but on the App Platform I receive:

with open(file.filename, "wb") as f:

******* PermissionError: [Errno 13] Permission denied

How can I fix this error? Any help is much appreciated. Thanks