The print app (SUNMI, USB, Android)

zrsPOS Print is a small Android app that turns the POS device itself into the printer server. It runs in the background, asks zrsPOS for receipts every few seconds and prints them on whatever printer the device has. Nothing is exposed to the internet and the store router is untouched.

Use it when the printer is built into the POS device, plugged into it by USB, or reachable on the LAN from it.

What it can print on

• The printer built into a SUNMI Android POS. The app talks to SUNMI's own printer service, so it reads the real paper width from the device and never guesses.
• A USB printer that follows the USB printer class (interface 0x07) — most 58 mm and 80 mm thermal printers. Plugged into the POS device or into a small Android box.
• A network printer on the same LAN that accepts raw ESC/POS on port 9100.

SUNMI devices

Any SUNMI Android device with a built-in printer works, because detection goes through SUNMI's own printer service rather than a per-model list. The common ones:

You do not have to tell zrsPOS which one you have. When the app pairs, it asks the device for its model and paper width and sends both; the receipt is formatted for that width.

Requirements: Android 7.0 or later, and the device must reach the internet.

Installing the app

The app is not on Google Play. Download it from zrspos.com/downloads.

1. On the POS device open a browser and go to zrspos.com/downloads.
2. Press Download APK. The file downloads.
3. Open the downloaded file. Android asks whether to allow installing apps from this source — allow it, then press Install. On SUNMI devices this permission is usually already granted.
4. Open zrsPOS Print from the app list. The pairing screen appears.

The download page always serves the newest version and shows the version number. To update, download again and install over the top; pairing is kept.

Pairing the app with your shop

In the Shopify admin:

1. Open zrsPOS → Setup guide → 7. Printers.
2. Press Add printer.
3. Under Connection choose Print app — on the POS device or the zrsPOS box.
4. Press Generate the pairing code. A QR code, the shop name and a 6-digit code appear. The code is valid for 10 minutes and works once.

On the POS device, in the zrsPOS Print app:

1. Press Scan the QR and point the camera at the code on screen. The shop and the code fill in by themselves and pairing starts. Or type them by hand: Shop (yourshop.myshopify.com) and the 6-digit code.
2. Name this device — optional, for example "Counter 1". It is what you will see in the printer list.
3. Press Pair.

The app says Paired ✓ — n printer(s) registered. In the Shopify admin the wizard shows the printers it found within a few seconds; finish the wizard and press Print test on the printer's page.

If the app says the code is invalid or expired, generate a new one in the wizard. Each code works once.

After pairing

The app's one screen shows:

• the state — "Printing for n printer(s) — connected to zrsPOS" when all is well, or the reason it cannot connect;
• the printers it drives, each with its status: ready, no paper, cover open, unreachable, error. The same status appears on the printer's page in zrsPOS;
• Local test print — prints a sample straight through the driver, without the backend. Use it to prove the printer itself;
• Allow running in the background (battery) — appears when Android battery optimisation would kill the app. Press it and allow. Do this, or printing stops when the screen is off;
• Unpair this device.

The app starts by itself when the device boots and runs as a foreground service, so there is a permanent notification showing it is connected. That notification is what keeps Android from stopping it; do not turn it off.

USB printers

1. Plug the printer into the POS device (a USB-A port, or an OTG adapter on a tablet) and switch it on.
2. Open zrsPOS Print. Android asks Allow zrsPOS Print to access the USB device? — tick "always" and allow. Nothing is detected until you do.
3. The printer appears in the app's printer list. If you are already paired, press Local test print to confirm, then pair again (or use Add printer in the wizard) so the new printer is registered in zrsPOS.

The paper width of a USB printer cannot be read from the device. Set it on the printer's page in zrsPOS, under Paper width.

Troubleshooting

Removing a device

Press Unpair this device in the app, and delete the printer in Setup guide → 7. Printers. Deleting the printer in the admin also revokes the app: it will say so on its next contact.