Should you have more than one networks in your restaurant/pub, you might encounter certain communication issues between the devices and/or printers. Most probably, the printers and devices are not connected to the same network. In order to verify this, you will need to compare the IP addresses of the devices in question and make sure that they are all on the same network.
Click here for detailed steps on how to find out the IP address on a computer
Click here for detailed steps on how to find out the IP address on a phone/tablet
Click here for detailed steps on how to find out the IP address of an Athlos/Epson fiscal printer
What you need to verify is that the first 3 sets of digits are identical on all of the devices. For example, a standard IP address would look like this: 192.168.0.100. The first 3 sets of digits (i.e. 192.168.0.) need to be exactly the same on all of the devices that you are using (printers, PCs, tablets, phones)