Making an POST of a FILE to an API call

I added a REST API config to a GPT I created, and I can use it effectively with most GET endpoints and the POST endpoints that post JSON data.

There is an endpoint that can POST a photo to relate it to an EVENT in the API.
I uploaded an image to the GPT, and asked it to extract some data, make some API calls, and then upload the image to the photo endpoint.

Is this something anyone has done successfully? I keep getting the
ResponseTooLargeError. Which, if I test the endpoint with the same file, just returns a small 200 response, so I don’t think the error is correct. Any tips on how to debug this?