What you need
A thermal receipt printer your counter device can already print to through its operating system — for example a printer installed on the computer, on your Wi-Fi network, or paired to the device in its system settings. NextUp Walk-in uses the system print dialog, so your device's own drivers do the talking to the printer; there is no special driver to install for the NextUp app.
Choose 80mm or 58mm paper per location. Both are supported, with a full itemized receipt laid out for that width.