Cannot upload binary file (.apk) to Developer Dashboard

I want to upload an Oculus Quest app devloped with Unity. As it's specified in the documentation:

1. I've prepared AndroidManifest to be compatible with Oculus Quest
2. I've created the keystore in Unity
3. I've exported the project to Android Studio, building the .apk from there and using the keystore generated by Unity

But after uploading to Developer Dashboard the .apk file generated with Visual Studio I'm getting the message
'The provided launch file (build.apk) was not found in the package'

If I'm only uploading a file (.apk): Which file is the initial file?
Do I have to write the name of the file (build.apk) in the form input 'Initial file'?