Had the exact same problem using the Youtube Data API, but no native Node there to save me 
Turns out, by looking at how other Google Node were implemented in the github repo (credential folder), I found that Google credentials need to be set at “Body” in the Authentication dropdown not “Header”
And then it worked like a charm !
You can also regularly schedule a simple get call in order to refresh the token (if like me you are in test and your refresh token expires after 7 days of inactivity)
Hopes it helps someone !