Android Studio Run/Debug configuration error: Module not specified

Resync your project gradle files to add the app module through Gradle

1. In the root folder of your project, open the settings.gradle file for editing.

2. Cut line include ':app' from the file.

3. On Android Studio, click on the File Menu, and select Sync Project with Gradle files.

4. After synchronisation, paste back line include ':app' to the settings.gradle file.

5. Re-run Sync Project with Gradle files again.

never mind, i changed the name in settings.gradle and synced and then changed it back and synced again and it inexplicably worked this time.