Hello
Did you previously generated an APK using this template? Or is the first time?
The Native template must have a folder structure like this repo:
https://github.com/mendix/native-template
It may be easier start from scratch again defining a blank folder in the Build Native App:
The Native Template folder structure will be generated again from the original Mendix Git Repo and you can apply your customizations to this template if needed.
Good luck!