Hi
There isn't such a limitation to Pro Trail account. I would suggest you check these things below.
1. Use exactly the same user who can log in Power BI.
2. Register your app in the same tenant with Power BI, which couldn't be like this: onmicrosoft.com and yourdomain.com.
3. Did you grant the permission in the Azure? You need to click the "Grant Permission" button explicitly.
4. The user should have the Edit permission of the App workspace.
Best Regards,
Dale