You can follow the following steps to try it out：
1. Disconnect the Bluetooth by clicking D30 (printer model/SN number) in the Bluetooth list of your cell phone. (WARNING: Do not pair Bluetooth again in your cell phone's Bluetooth list.)
2.Turn on your phone's Bluetooth and enter the App. Then click the Connect button on the top right corner of the App to reconnect your printer to the App.
Operation video link:
If the above doesn't help, here are some basic troubleshooting methods:
1. Make sure Bluetooth is turned on in the Quick Switch or Control Center page, and then connect the printer in the Print Master App.
2. Make sure that all permissions are allowed when you install the application, or you can turn them on in your phone's Settings.
3. Use a thimble or similar tool to poke out the round hole next to the power port. and try to restart the printer and the phone.
4. Please try to download Print Master with another cell phone to see if you can connect to the printer.
If this still does not solve the problem, please provide us with the following information to check.
1. Your cell phone model and system version.
2. Print Master APP version.
3. The SN begins with Q for the printer. (Turn on the printer and double-click the printer power button to print the self-test page.)
4. Order number and time of purchase.
5. You can record a video that operates the APP to search for problems connecting to the printer.
We will give feedback to our technicians for analysis.