from typing import Annotated

from fastapi import FastAPI, Path, Form
from pydantic import BaseModel
import base64

class file(BaseModel):
    name: str
    data: str

app = FastAPI()

@app.post("/upload")
def upload(filename: str = Form(...), filedata: str = Form(...)):
    image_as_bytes = str.encode(filedata)  # convert string to bytes
    img_recovered = base64.b64decode(image_as_bytes)  # decode base64string
    try:
        with open("uploaded_" + filename, "wb") as f:
            f.write(img_recovered)
            print('fine')
    except Exception:
        return {"message": "There was an error uploading the file"}
        
    return {"message": f"Successfuly uploaded {filename}"}

Backend Output:
INFO: Started server process [18183]
INFO: Waiting for application startup.
INFO: Application startup complete.
INFO: Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
INFO: 127.0.0.1:45202 – “GET /docs HTTP/1.1” 200 OK
INFO: 127.0.0.1:45202 – “GET /openapi.json HTTP/1.1” 200 OK
fine
INFO: 127.0.0.1:49262 – “POST /upload HTTP/1.1” 200 OK

I tried using BaseModel and many other data types.