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 sample curl request:

curl -H "Content-Type: application/json" -X POST -d '{"range":"A1","majorDimension":"ROWS","values":["Frank2"]}' https://sheets.googleapis.com/v4/spreadsheets/{SPREADSHEET_ID}/values/A1:append?valueInputOption=RAW&key={API-KEY}

Here's the response:

{
  "error": {
    "code": 401,
    "message": "The request does not have valid authentication credentials.",
    "status": "UNAUTHENTICATED"
  }
}

Can this be done only using an API Key or am I doing something wrong? The documentation suggests it is possible if the spreadsheet is shared publicly.

Answer 1

Requests that write to the spreadsheet require authentication credentials. Even if the spreadsheet is shared publicly, when writing through the API the write must be attributed to a user.

Answer 2

This is currently broken. You can not edit the document (even if public) with only an APIKey.

https://issuetracker.google.com/issues/73974970