Thanks for the tipp... as i also use my old galaxy s3 with android 8, where there is nothing necessary to be saved on this one, i will probably try this tomorrow (installing afert upgrading to 6.5.2 did not work...)That is because of signing differs from previous installed versions of FreeFlight6!
On my Huawei Android 9 tablet i have exact your problem to install patched version. No hint were given during installation process but adb-installation gives me the correct hint. I guess your phone/tablet Version is Android 9?
Uninstalling of previous version of FreeFlight6 (Playstore) will not work without erasing footprints.
I did not investigate further and have done a quick factory reset (was brand new). After this it was of course no problem to install patched Freeflight6. I've used the app patched by myself because my signing differs to ds2atc and i want to switch back and forward for testing.
Maybe ds2atc can help here...
Regards
So if i understand you right i do not have to have a free flight 6 to be installed on the phone before i install the patched version?