1) What exact error are you getting when you try to QR provision?
If you're getting: "Could not setup QR detector", this means your Google Services on your phone our out of date. Please go to your Google Play app, top left settings, "Games and Apps" and update your Google Services.
If you're getting any other error, this means your PBX's FQDN could not be resolved by your mobile device (or rather the wifi it's connecting through) and so the provisioning file is not reachable. This is a DNS issue not an app issue. We'l look into making this more obvious to the user in a future version.
For the actual provisioning file, if you have downloaded it to your device, then you'l need Total Commander, find the provisioning file and open it using 3CX.