Json body + multiple image post request fastapi

Question

I am new to API development. Using fastapi to create one. I would like to create post request which accepts following JSON and multiple image files.

{   "data": {
 "cId": "6351ata0b3ab4640fe595433ed6",
 "datain": {
   "diameter": 50,
   "tolerance": 20
 }   } }

However I get:

422 Unprocessable Entity.

How should I do it?

I tried to do as following:

class Det(BaseModel):
    diameter: int
    tolerance: int

class CalData(BaseModel):
    cId: str
    datain: Det


@app.post("/api/process_image")
async def process_image(
    caldata: CalData = Body(...),
    files: list[UploadFile] = File(...),
):