DIAGNOSIS The tape feed mechanism is obstructed. A small piece of torn tape backing or a misaligned cartridge is jamming the gears.
FIX Immediately power off the P21. Open the tape compartment and remove the cartridge. Inspect the orange plastic feed gears inside the machine for debris. Use tweezers to remove any visible fragments of tape or paper backing. Inspect the cartridge itself. Ensure the white plastic tape roll spins freely and the tape feeds smoothly from the center, not the side. Reinsert the cartridge, ensuring it snaps into place squarely.
IF THAT DIDN'T WORK The gear mechanism may have a worn or broken tooth. This requires disassembly. The symptom is a repetitive click-grind at the same point in each rotation. This is a hardware failure.
HEADS UP Never force the tape cutter lever if you hear grinding. This can strip the plastic gears. Always use the app's cutting command or feed button to advance tape before using the physical cutter.