Full Error Message: 
“Error while creating new document. Error message: Error getting access token. Error: invalid_grant. Error description: Token has been expired or revoked”
Reply: 
1. You may be getting this error message when trying to generate a document and your Salesforce custom domain name has changed or you have a new server instance (example NA18).
2. Go to RS Documents Configuration tab and click “grant access” to reauthorize app and google drive.
3. From there see if you receive an error message referring to “Error: redirect_uri_mismatch” please copy/paste the full error message and email it to support@ramseysolutions.com so we can add your updated custom domain/server instance to our approved list of URLs.
4. After your custom domain URL has been added by support, you can continue with authorization and document generation.
NOTE: If you did not see an error message when going to RS Documents Configuration tab, please submit a free case to support with the error message, your Salesforce org ID and your detailed steps for Support to recreate the error message once logged in (grant login access to Ramsey Solutions).