Read a custom GATT service and characteristic from my tensiometer (BPM) with BLE)

Hi guys. i have a problem. I have a tensiometer that shows the blood pressure measurements and my ionic app read his services (like device name, manufacturer, batery level, etc), but the device has som custom GATT services that doesn’t appears in the bluetooth official GATT services list. when i try some one custom services, my app disconnect inmediatly the tensiometer. then ¿How i can read a custom service without problem?