When trying to import from Google Drive, the following error is shown:

The token used to identify you with Google Drive was not valid: "message from google".

The token used to identify you with Google Drive was not valid.

Any error code ending in -233

The token used to identify you with Google's servers was invalid. This often happens when it has expired and ShareGate Migrate is still using it. Here is what Google has to say on this error:

401: Invalid Credentials
Invalid authorization header. The access token you're using is either expired or invalid.

You should try to reconnect your Google Drive account with ShareGate Migrate, and re-start your migration if this error ever occurs.