Error Message:
“Error while creating new document. Error message: Error: 403. Error description: { “error”: { “errors”: [ { “domain”: “global”, “reason”: “forbidden”, “message”: “Insufficient permissions for this file”, “locationType”: “other”, “location”: “file.permissions” } ], “code”: 403, “message”: “Insufficient permissions for this file” } }”

-This error can happen when clicking button to generate document and you do not have sufficient access to the google doc template, the google drive folder or the google drive account being used.

How to Resolve:
1. Check your sharing settings in Google Docs template and make sure not set to “private.” See this Google Docs article for more detail on choosing your sharing settings though most popular setting is “anyone with the link” under “Advanced” sharing settings.
NOTE: If you do not see this Google Doc sharing setting “anyone with the link” under your Advanced sharing settings, then you have some strict company drive settings and you will need to have the Super Admin modify them or use a different Google Drive account for app, you can refer to this article for more detail.
2. If you are accessing the template from a Google Drive folder (meaning you put Folder ID in document action), you need to make sure the sharing settings are modified on the folder as well. You need to have edit access to the folder in use or be owner of the folder if you would like to generate documents there.
3. If you modified the visibility setting to “Company” and then you get an error message that displays in document action, you can see this article for more detail and needing a Google Apps For Work Account.
4. If you checked steps 1-3 and still unable to resolve, make sure you did the following standard steps:
-Updated custom button code to match what is in document action
-Check that your Google Doc template that is being used in document action is stored on the same Google Drive that is authorized under your Salesforce user.
5. It is possible that you are using another app functionality with RS Documents app and record may have been deleted which would cause error message. Test process again to make sure record not deleted and see if error persists. 

-If you need more information on google drive or doc sharing settings, you can this article.