C# Power BI API 401 Unauthorized ServicePrincipalIsNotAllowedByTenantAdminSwitch

Ok I solved this, my problem was with the RSL. (Roles)

My dataset, it was configure with a Dynamic Role, and I didn't know it. actually  just few Users were on that Role. so I was getting that error because that.

I was using on this line of code, which only works when your dataset is not Identity required.

GenerateTokenRequest generateTokenRequestParameters = new GenerateTokenRequest(accessLevel: "view");

How do I resolve it?

1.- Make sure your Dataset is or not Identity Required(Using RLS).  Use the next two lines to evaluate:

if (dataset.IsEffectiveIdentityRequired == true){
//"This report is Identity Required. Make sure to Provide a Valid Username."
}
if (dataset.IsEffectiveIdentityRolesRequired == true) {
//Do your validations
//"This report is Identity Roles Required. Make sure to Provide a Valid Role(s)."
}

If is Identity Required, then you will need the Username(email) and the Roles,  as far as I know Dynamic is the default Role, but the PowerBI Report developer should know this information. So do the next on code:

 var rls = new EffectiveIdentity(Username, new List<string> { dataset.Id });
                if (!string.IsNullOrWhiteSpace(Roles))
                {
                    var rolesList = new List<string>();
                    rolesList.AddRange(Roles.Split(','));
                    rls.Roles = rolesList;
                }
                var generateTokenRequestParameters = new GenerateTokenRequest(accessLevel: "view", identities: new List<EffectiveIdentity> { rls });

Send  the  GenerateTokenRequestParameters variable to the function to get the EmbedToken,

as next:

var TokenResponse = await client.Reports.GenerateTokenInGroupAsync(WorkspaceId, report.Id, generateTokenRequestParameters);

You should be good to go with those actions.