Refresh Failed: DMTS_OAuthTokenRefreshFailedError

Hi, WesleyvB 

You need to make sure the gateway is working first. This is an Application and you will need to download and install the gateway Application you need:

Install an on-premises data gateway | Microsoft Learn

Then open the Application:

If there is a new version available, it will prompt you on the Application page.

Then in Power BI Service click on Settings (gear button) and then select 'Manage Connections and gateways' to go to the gateway management screen. 

You will need to check that the gateway connection you are using is online before you can go and change the credentials, and in the meantime you will want to make sure that the credentials you have entered are correct.

I hope my suggestions give you good ideas, if you have any more questions, please clarify in a follow-up reply.
Best Regards,
Fen Ling,
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