[Python] FastAPI raises 422 Unprocessable Entity error when uploading File through Postman

I am using a POST request for uploading a file to a FastAPI application through Postman and save it to my local directory. However, a 422 (Unprocessable entity) error occurs, as shown below:



In Postman, I selected the binary option to upload the file, as you can see in the image above.

Below is how my FastAPI backend looks like:

main.py

from fastapi import FastAPI
from api.endpoints.vendor import router

app = FastAPI(title='Vendor Acknolegment API')
app.include_router(router, prefix='/vendor', tags=['vendor confirmation'])

if __name__ == '__main__':
import uvicorn
print("entered here")
uvicorn.run("main:app", host="0.0.0.0", port=8000,
log_level='info', reload=True)



vendor.py

from fastapi import APIRouter, status, File, UploadFile
#from lxml import etree
import os

# file path
UPLOAD_DIR = r"c:\ack"

# check if the directory exists.
os.makedirs(UPLOAD_DIR, exist_ok=True)

# creates the endpoint path
router = APIRouter()

# POST Ack
@router.post("/ack/", status_code=status.HTTP_201_CREATED)
async def upload_ack(file: UploadFile = File(...)):
# define the complete path where the file will be saved.
file_location = os.path.join(UPLOAD_DIR, file.filename)

with open(file_location, "wb") as f:
f.write(await file.read())

return {"message": f"The file '{file.filename}' has been successfully saved into the server."}

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