Welcome to the ODK forum, @GAMPINI! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!
The OData feed is intended primarily for connecting to submission data (that is, for analysis and visualization), and not for submitting data. What is your use case that you are trying to submit data using the "project's API OData code"? Most people submit using either the Android app ODK Collect or Enketo web forms in their browser.