Power Bi Embedded - SKU EM1 or EM2 ?

Hi,

i'm a little confused with all the informations we can read about the power BI Premium SKU EM. So i try this community to find a solution .....

We developped a web portal to embed some Power Bi Reports and Dashboard. This web portal is only available for internal usage, and we used the service principal method to authenticate our app to Power BI. As i could read, for this use case, we need the Power BI Premium SKU EM1, 2 or 3. am i right ?

But how Power BI manage licences with the service principal authentication, because currently the web portal is running (in test mode) and users without power bi licence (pro or free) can display and consume reports. Reports we display in our web portal are in a workspace without a capacity. I read that in production mode we need a capacity, but wich one ? SKU A is for external users only as i  understand and SKU EM is for internal users ? But how and where can i subscribe a SKU EM1 or EM2 ?

Thanks a lot for any informations which can help me !