The print app (SUNMI, USB, Android)

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

Use it when the printer is built into the tablet, plugged into it by USB, paired with it by Bluetooth, 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 tablet 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 tablet or into a small Android box.
• A printer that charges the tablet — a receipt printer with a USB port for tablets (for example an Epson TM-m30II-SL in a tablet stand), where the printer powers the tablet over the same cable. Needs zrsPOS Print 1.0.8 or later.
• A Bluetooth printer paired with the tablet in Android's settings. Needs zrsPOS Print 1.0.9 or later.
• A network printer on the same LAN that accepts raw ESC/POS on port 9100.

SUNMI tablets

Any SUNMI Android tablet or terminal 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 tablet for its model and paper width and sends both; the receipt is formatted for that width.

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

Installing the app

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

1. On the tablet 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 tablets 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.

Updating the app

The app updates itself from its own screen; you do not download anything again.

1. Open zrsPOS Print and press Check for updates. When a newer version exists, the app says so (it also shows a notification).
2. Press Update to … (the button names the new version). The app downloads it and checks it.
3. The first time, Android asks to allow this app to install its own updates: allow it on the screen that opens, come back to the app and press Update to … again. Android only asks once.
4. Confirm Install on the Android screen. Printing resumes by itself afterwards, and the pairing is kept.

If the update fails, the app says why; try again, or download the newest version from zrspos.com/downloads and install it over the top. The pairing is kept either way.

Pairing the app with your shop

In the Shopify admin:

1. Open zrsPOS → Settings › Printing & delivery › Printers and press Add printer.
2. Under How it gets receipts choose Print app or zrsPOS PrintBox and press Next.
3. Choose the store and a name, then press Next: pairing code. A QR code, the shop name and a 6-digit code appear. The code is valid for 10 minutes and works once; the page counts the minutes down and offers a new code when it runs out.

On the tablet, 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 of 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, Paired shows by itself within a few seconds, with the printers it found. Press Next: test print and print a test.

If the app says the code is invalid or expired, make a new one on the same page. 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 tablet (or the box) starts up 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.

How often it asks for receipts

By default the app asks zrsPOS for work every 2 seconds. You can change it on the printer's page in zrsPOS, under Asking for work › How often (every second up to every 30 seconds). It takes effect on the app's next contact; nothing to reinstall. Shorter means receipts come out sooner; longer is kinder to a battery-powered tablet and to a quiet shop's data.

USB printers

An Epson TM-m30, TM-T20 or TM-T88, or any 58/80 mm printer of the USB printer class, plugged into an Android tablet or a SUNMI. The printer must be self-powered (mains); the tablet only carries the data.

1. The cable. The printer has a USB-B socket. From a tablet with USB-C use a USB-C-to-USB-B cable, or a USB-C OTG adapter plus a standard A-to-B printer cable. From a SUNMI with USB-A, a plain A-to-B cable.
2. Charging. With an ordinary printer cable the tablet powers the USB port, so while the printer occupies the tablet's only USB-C port the tablet does not charge. For an all-day counter use a USB-C hub with power passthrough (Samsung tablets accept a PD hub), a tablet with a charging dock, or a printer that charges the tablet (next section).
3. Plug it in, switch it on. Android asks Open zrsPOS Print when this USB device is connected? — tick Use by default and allow. That is the whole permission: it is remembered across reboots and re-plugs. (If the printer was already plugged in when you installed the app, open the app once; it asks the same question.)
4. The printer appears in the app's printer list within seconds; the agent registers it in zrsPOS by itself. Press Local test print to confirm, then Print a test on … on the printer's page in the admin to confirm the round trip.

The paper width of a USB printer cannot be read from the printer; new USB printers are registered as 80 mm. For a 58 mm printer set it on the printer's page in zrsPOS, under Paper width.

Epson printers only: if the printer is not found although the cable and power are fine, the printer's USB mode may be set to Epson's vendor class rather than printer class. zrsPOS Print accepts both, but some very old firmware exposes neither — Epson's TM Utility app shows and changes the setting.

Printers that charge the tablet

Some receipt printers have a USB port for tablets and power the tablet through it — for example an Epson TM-m30II-SL in a tablet stand. Here the printer is in charge of the cable, and Android sees it as a USB accessory rather than a USB printer. zrsPOS Print 1.0.8 or later prints to it.

1. Connect the tablet to the printer's tablet port and switch the printer on. The tablet starts charging.
2. Android asks whether to open zrsPOS Print for this USB accessory. Allow it, and tick Always (or Use by default) if offered. If Android offers another app instead (Epson's TM Assistant, for example), clear that app's defaults in Android's settings, unplug and plug in again, and choose zrsPOS Print.
3. The printer appears in the app's printer list. Press Local test print, then Print a test on … on the printer's page in the admin.

Only one app can use the printer over this cable. If Shopify POS should also print to the same printer, give it the printer's network connection instead.

Bluetooth printers

zrsPOS Print 1.0.9 or later prints to a receipt printer paired with the tablet over Bluetooth.

1. Pair the printer first, in Android Settings → Bluetooth, as for any Bluetooth accessory. The app does not search for printers; it uses the ones already paired.
2. Open zrsPOS Print. If it shows Allow Bluetooth (nearby devices), press it and allow. (If Android no longer asks, the app explains: under Permissions, open "Nearby devices" and choose Allow.)
3. The paired printer appears in the app's printer list and is registered in zrsPOS by itself. Press Local test print, then Print a test on … on the printer's page in the admin.

The app keeps the Bluetooth link to the printer open between receipts and closes it after 5 idle minutes. Most receipt printers accept only one Bluetooth connection at a time, so do not share that printer with another tablet, or with Shopify POS's own Bluetooth printing. If Shopify POS also needs the printer, connect it by network or USB for Shopify.

Under the printer list the app says what it sees over Bluetooth: the paired printers, "not allowed", "off" (turn Bluetooth on in quick settings) or "no paired printer".

Troubleshooting

Removing a tablet or a box

On the printer's page in zrsPOS (Settings › Printing & delivery › Printers › the printer), press Unpair the print app. The app is signed out for good: it says so on its next contact and never comes back by itself. Its printers stay saved, not in use. To print with it again, pair it again with a new code from Add printer.

On the tablet or PrintBox itself, Unpair this device in the app signs it out from that side; unpair it in zrsPOS too, so the admin no longer counts on it.

Deleting a printer does not bring it back either: the app does not add it again. Deleting the app's last printer in use also signs the app out.