Power BI Reporting Server Authentication type Integrated not supported

[adv]

Hello,

We are testing Power BI Reporting Server. We want to be able to access the dashboards from the computers from the LAN connected to the domain. Currently we have are testing a SSAS data base. When the DB is on the same server as the Power BI Reporting Server, we are able to see the dashboards. When the DB is on an other server we have an error message:

Something went wrong.

We couldn’t run the report because we couldn’t connect to its data source. The report or data source might not be configured correctly.

With the following details:

We couldn’t connect to the Analysis Services server. The server forcibly closed the connection. To connect as the user viewing the report, your organization must have configured Kerberos constrained delegation.

We followed these steps https://docs.microsoft.com/en-us/power-bi/report-server/configure-kerberos-powerbi-reports

But it didn't solve our problem completely. It doesn't work with "As the user viewing the report":

If I choose "Using the following credentials" and I enter manually any domain user and password, it works.

We are out of ideas. Where is the problem?

Thank you!