15.5 legacy app descripción

Use only if you are unable to update 3CX Server to Version 16
For use with Version 15.5 only
Can work on Android 6,7,8
Will have problems on Android 9
Does not work on Android 10

The proper app you should use is this:
https://play.google.com/store/apps/details?id=com.tcx.sipphone14