When I run a Xamarin project, I get the error Could not find the android.jar file for the R API level, how can I fix it?

Question

Android

Good afternoon, when I try to run a Xamarin project, I get the following error:

The android.jar file for the R API level could not be found. This means that the Android SDK for the R API level is not installed. Install it in the Android SDK Manager (Tools > Android > Android SDK Manager…) or modify the Xamarin.Android project to target the installed API version. (C:\Program Files (x86)\Android\android-sdk\platforms\android-R\android.jar is missing.)