This also applies to SAB.
I set RAB to download audio from the internet instead of including it in the APK. When I built the app after that and asked it to download an .mp3, it would crash, or say to check my internet connection.
Turns out the issue was that I had not included the https:// (or http://) in my Web Address in the Edit File Source window. Once I added that, it worked fine.
Here are some other troubleshooting tips @Marty Lang gave me that you can try if you are still having trouble.
In your filenames:
-Use all lowercase
-Don’t use any diacritics, special characters, or even ñ.
-Don’t use any spaces