See FAQs for more information on Nemonic products.

Program error(Mobile)Android - A message keeps on 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 continues, disable and enable Bluetooth again from your smartphone.

If the trouble insists, do as follows:

From your smartphone/tablet, go to Settings > Connection > Bluetooth, and disconnect the Nemonic printer. Then, try to reconnect it using the app.