OBD2 bluetooth CARISTA adapter

[dentist69]

I have fitted a new rear caliper with motor for epb (purchased on ebay) and purchased a Bluetooth obd2 adapter that comes with a full diagnostics app called carista as was made aware i would need to reset the cars ecu to tell it i had fitted a new caliper.
I was pointed in the direction of this app via a vw page on Facebook and attracted to it as it comes with a free months trial.

However

After fitting caliper and successfully bleeding brakes I set about plugging in the carista obd2 and logging into the app.

I have absolutely no doubt there is nothing wrong with the carista as have successfully used it to change some parameters ie when lights come on, dings when locking, I even fixed the unlock button on drivers door and found an error code I didn't know existed and repaired that......

Whenever I try to open or close the parking brakes or want to reset them thus telling the ecu that new caliper is fitted it comes back with cannot connect to vehicle try turning ignition on and off and trying again??? I have had a lot of feedback and know one is having any problems with carista for everyone I've connected with it works fine!

Any ideas??