Follow these steps to reset the Bluetooth chip in your SumUp card terminal:
Turn off Bluetooth on your smartphone or tablet.
Close the Paymash app.
Make sure your card terminal is not charging.
Turn off the SumUp device.
Now press and hold the power button on your card terminal until "Release for BT" is displayed.
Release the power button as soon as you hear a beep.
Reconnect your card terminal to the Paymash app.
For more information on connecting your SumUp device to the Paymash app, see the article Connecting SumUp Card Terminal.