Google Sheets API v4 append request receives HTTP 401 response for public feeds using API Key

Question

This is extremely similar to another question answered here about how to GET spreadsheet data, but I\'m trying to append data to a spreadsheet. Here\'s my s

Answer 1

https://developers.google.com/sheets/api/guides/authorizing#APIKey

The page above states the following:

Your application must use OAuth 2.0 to authorize requests. No other authorization protocols are supported. If your application uses Google Sign-In, some aspects of authorization are handled for you.