Help Needed: Google Document AI - CREDENTIALS_MISSING / invalid_scope Loop with HTTP Request Node

Questions
1

Hello n8n Community,

I am trying to connect to the Google Document AI API using the HTTP Request node, and I’m stuck in an authentication loop. I would be grateful for any help.

My Setup:

  • n8n Version: 1.98.2 (Cloud)
  • Goal: Call the Document AI :process endpoint.
  • Credential Type Used: Google Service Account API

What I Have Verified on Google Cloud:

  • The Document AI API is enabled.
  • A Billing Account is active and correctly linked to the project.
  • A Service Account exists with the Document AI Administrator role.
  • A JSON key for this service account has been created, downloaded, and is active.

The Problem in n8n:
I have created a Google Service Account API credential, successfully pasting the client_email and private_key from the JSON file.

In my HTTP Request node, I use this credential. The rest of the node (URL, Body, etc.) is configured correctly. However, I face a catch-22 depending on one switch in the credential’s configuration:

  • Scenario 1: When the credential’s Set up for use in HTTP Request node switch is OFF, the API call fails with a 401 - CREDENTIALS_MISSING error.

  • Scenario 2: When the credential’s Set up for use in HTTP Request node switch is ON, the API call fails with a 400 - invalid_scope error.

I have spent many hours debugging this and have verified every setting on the Google Cloud side. It seems like a potential bug or issue with how this credential type interacts with the HTTP Request node in this version of n8n.

Could anyone advise on a solution or a workaround? Thank you very much.