com.android.ide.common.process.ProcessException: Failed to execute aapt error
Any ideas what's causing this:
This issue seems to be specific to 4.21
Solution is to go to Project Settings > Platforms > Android SDK and set SDK API Level and NDK API Level both to 'latest'.
You also need to have CodeWorksforAndroid-1R7u1-windows installed. If you have android studio or anything else that uses android, don't put updates on the same folder. UE needs the exact versions in 1R7u1
Follow this question
Once you sign in you will be able to subscribe for any updates here