Both Google products, Google Sheets and Google Data Studio are affected by an issue at Google's account management. (Being logged into multiple Google accounts in your browser at the same time is what can cause this issue.)
A temporary solution before Google releases a fix, is to log out all users from Google in your browser except for the one account you need to work the product/use the license (for example, for Google Sheets, log out all users except the one attached to the Supermetrics license). Then try to log in to the data source again. To log out of Google accounts, click on your icon and click on sign out of all accounts.
Alternatively, if logging out all users is a hassle, you can also do this via Incognito/private browsing.
If you'd like to help speeding up the fix from Googles side, please click on the star in this Google Bug report. More votes means it goes up in their urgency.
We appreciate your help.