Hi Joanna,
Greetings from Syncfusion.
Query 1: Does not recognize the license when placed in App.XAML.cs
For registering the license key, refer the below documentation link.
Query 2: Error using SfCarousel control.
We suspect this error is raised is due to the lower Xamarin Forms installed in your project. As we have upgraded our controls to Xamarin Forms 3.1 version from the 17.1.0.38 version as mentioned in the release notes link below.
So, we request you to upgrade and confirm us whether the issue is resolved.
Thanks,
Rachel.