1. Check if the APP device is connected. If not, please turn on the bluetooth of your phone. Make sure that no one else is connected to your printer.
2. Check if the print head is overheated, if yes, try to print again after it cools down.
3. Check the tightness of the paper roll, and replace after it is manually rolled (not too tight).
4. Check whether the paper is on the roller. If not, please extend the paper to it.
5. Restart the printer. If the problem still exists, short press the Reset button, restoring to factory settings.