API Buildship input too large / cannot read properties of undefined (buffer)

Hi, I am trying to upload an image from Flutterflow via Buildship API to Firebase. I tested the API with Postman and it worked fine, meaning the settings in Buildship and Firebase seem to be ok.

But why doesn t it work when calling the API in Flutterflow? The image size is less than 800 KB. I followed the Flutterflow documenation. Do I need to change sometihng regrading the encoding of the JPG`or why wouldn t it read the "properties of undefined"?

Thanks a lot!