I get this these issues in the build:
/Library/Frameworks/Mono.framework/Versions/4.8.0/lib/mono/xbuild/14.0/bin/Microsoft.Common.targets: warning : Reference 'Facebook' not resolved
/Library/Frameworks/Mono.framework/Versions/4.8.0/lib/mono/xbuild/14.0/bin/Microsoft.Common.targets: warning : Reference 'Xamarin.Auth.iOS' not resolved
/Library/Frameworks/Mono.framework/Versions/4.8.0/lib/mono/xbuild/14.0/bin/Microsoft.Common.targets: warning : Reference 'HockeySDK' not resolved
.0/lib/mono/xbuild/14.0/bin/Microsoft.Common.targets: warning : Reference 'HockeySDK.iOSBindings' not resolved