Android Mobile Terminal does not support mobile devices with Android version 6.0 Marshmallow. It is not possible to support this system and using new technologies, supported by Google.
All users may update their mobile devices to Android 9.0 P. It is version, which will be accepted by most of the old mobile phones from the year 2016.
Here is a link to update: https://www.rootupdate.com/upd…hmallow-to-android-9-0-p/
If you will need support/advice on how to do it, please contact me using PM. I will send you details about your type of mobile device.