See FAQs for more information on Nemonic products.

Program error(Mobile)iOS - A message keeps displaying: Response time-out.

The connection may be lost temporarily due to the communication error.
Turn on and off the Nemonic printer. If the trouble insists, disable, and enable Bluetooth again from your smartphone.

If the trouble insists, do as follows:

From your iPhone/iPad, go to Home > Settings > Bluetooth > Nemonic Printer previously connected. Tap the (i) icon next to it at the right. Tap “Delete This Device” to remove it from the device list. Then, try to reconnect it using the app.