Sail POS: A card reader isn't working — troubleshoot it and take payments on another terminal

Common things to try first

If it's just one device having the issue, use a different terminal to keep taking card payments while you troubleshoot that one. If multiple readers are affected, escalate call to support technician.
Ask if terminal is using a swipe reader or chip card reader. Once answer is obtained, continue to relevant section down below.

Swipe reader (MSR) built into the terminal

Open Notepad (or any text field) on the terminal and have a card swiped through the reader — if it's working, a string of characters will appear. Nothing appearing means the reader itself likely isn't reading.
Reseat the MSR reader's cable connection, then restart the terminal.
Run a couple of test card transactions to confirm it's reading correctly.
Still not working after reseating and restarting? Call support.

PAX EMV device (tap/insert/chip, usually a PAX A35)

Power cycle the device: press and hold both the red "X" button and the green circle button together for a few seconds until the screen shows "restart," then tap the screen and confirm yes.
Once it restarts, confirm the payment app is running — it should auto-launch, but you can also open the BroadPOS app from the device's home screen to bring it up manually.
Run a test transaction to confirm it's working.
Still not working after a power cycle? Call support.

A test credit card transaction completes successfully on the affected device/terminal.

Payments failing on multiple or all terminals, but orders/items are still ringing up fine? That's usually an internet connectivity issue, not a card reader problem — check A network/internet outage — check power and reboot your network devices first. Fixing the connection often fixes the payment failures too, since a single bad reader almost never affects more than one terminal at a time.
Is there at least one other terminal that can take card payments? Yes — continue below, not an emergency.
All terminals/card readers are down, or cards are slow or not going through on every terminal (not just one device)? This points to the processor, not a reader. Processor-wide issues are often temporary and resolve on their own within an hour or two. If you need cards running normally right away rather than waiting it out, you can switch terminals to the backup processor yourself — see How to Switch a Terminal to the Backup Processor. Otherwise, skip to "When you must call."

Use a different terminal to take card payments while you troubleshoot the affected reader.

Reseating/restarting (MSR) or power cycling (PAX) doesn't resolve it
All terminals/card readers are down (emergency)
The processor itself appears to be down, or every terminal is slow/failing and switching to the backup processor didn't help or isn't enough, or you want to confirm this is a known processor outage — see How to Switch a Terminal to the Backup Processor

Once the reader is repaired/replaced, resume normal use — no further action needed.