The phone's bluetooth has timed out. Please do following,
- Ensure that you're within bluetooth range and try to operate the device again
- Turn off bluetooth from phone's settings and turn on. Try to operate.
- If problem persist and you're Android phone user then please try this,
- Go to Phone Settings > Apps & notifications > App info.
- Tap on the 3-dot overflow menu on the top-right and tap on Show system.
- Scroll down and Tap on “Bluetooth”.
- Now, press “Storage” and select “CLEAR DATA”
If problem persist, please submit an issue(PDQ Smart STP App-->Help--> Submit the issue)