You are not able to see the entities when you want to add a new entity,
or you encounter the following error by sync: Authorization failure: HTTP protocol error. 401 Unauthorized. Invalid Credentials,
or XcoreXgooglesheetsX190X7216.eff:  Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential, once the connection is created.
or XcoreXgoogleanalyticsX170X6417.aic: You must provide the OAuth access token. Refer to the help documentation to obtain the access token.
The most common reason for the above mentioned errors is, that you have added more than one connection from Gtmhub to the Google Data Source with the same Google account.
Google provides an access token refresh mechanism only for one connection per application. Therefore any subsequently added connection will work for a brief period of time.
To ensure the proper synchronization of your data - create all data sources using the initial connection that was added to your Gtmhub account. If you do not know which of your connections is the initial one you can remove Gtmhub`s access to your Google account like this:
Click on "Security" section in your Google Account and on "Manage third-party access"
If this is not an option you can contact our support team for instructions how to revoke previous connections.
We will take the following example:
You have created an initial connection to a Google Data Source. Let say you don't need it any more and you have deleted it. Currently the Data Source stays without connections. By adding a new connection to it, it will work again for a brief period of time as the token refresh mechanism is still associated with the initial connection, which you have already deleted.
For the new connection successful to work as expected please follow the above mentioned step 1 in this article.
Here is a short video how to add entity to the existing Google Spreadsheet connection:
Please note that I have added 2 connections to Google Spreadsheet. The primary connection is "test" and as you see I can add a new entity without problems.
But if I want to add a new entity for the second added connection with the same google account, I am not able to see the data source entities.
Here the video:
The sync for the second added connection does not work as well, because as mentioned above, token refresh mechanism works only for the primary connection -respectively the token for the second connection has expired.
Please make sure that you are using only one connection between Gtmhub and Google Data Sources.