Error HTTPS Azure site

I've created an ApiWeb site hosted on Azure. I also access the APIs via APP xamarin.forms. If I set HTTP, everything works properly, if I enable the HTTPS domain, I can no longer query the APIs from xamarin.forms.
Where am I wrong?

In Xamarin.Forms I have, for HTTP
public Uri UriBaseAddress = new Uri ("http://myfirstapp20180927022910.azurewebsites.net/api/");

for HTTPS
public Uri UriBaseAddress = new Uri ("https://myfirstapp20180927022910.azurewebsites.net/api/");