Help needed regarding N8N Gmail node using Google Service Account as auth

Hello!

I need help with 1 thing that I've been struggling with for a few hours.

Goal: send emails using the n8n Gmail node using the Google service account authentication.

When I enter the SA email and the private key, I don't get any errors yet, but when I toggle ON the "Impersonate a User" button and enter my Google Workspace email, then I get this error:

Private key validation failed: 401 - {"error":"unauthorized_client","error_description":"Client is unauthorized to retrieve access tokens using this method, or client not authorized for any of the scopes requested."}

And I don't know how to fix it.

Additionally, I tested my credentials using JavaScript in my local code editor, and everything worked flawlessly.

I would at least appreciate some material from which I can learn.

By the way, I have already read the official documentation.

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Help needed regarding N8N Gmail node using Google Service Account as auth