Unable to install APK on Oculus Quest

Hi.
We're experiencing an issue while trying to develop for the Oculust Quest using Unreal 4.24.3. The apk builds fine (Android SDK v 23 and 21 tested), but after being transferred to the OQ it will not install.

The Log.txt indicates this as the error:

ProcessResult.StdOut:   Performing Streamed Install
ProcessResult.StdErr:   adb: failed to install filename_with_path.apk:
CommandUtils.Run: Took 0.4808586s to run adb.exe, ExitCode=1
... 
Log.WriteException: AutomationException: Installation of apk 'filename_with_path.apk' failed
...
Program.Main: AutomationTool exiting with ExitCode=35 (Error_AppInstallFailed)

The device is in developem mode, and accepts unknown sources too.

Any ideas, anyone?