The Visma Severa API driver uses the SOAP-driver, which is in maintenance mode currently. A small change was not included for the SOAP. This has been corrected. Please try again.
Also note that many Visma Severa APIs may return an error from Power BI since they require a parameter, but the requiredness of these parameters can not be extracted from the Visma Severa API metadata.
For instance the table Severa.API.ContactsChangedSince@sva requires a date. Selecting it from Power BI will return an error: