Every Genius device has to be on the location network before the POS app will do anything useful.

The rule that catches people out

Genius NextGen and Mobile 2.0 devices do not support WPA3. Use WPA2. WEP also works but should not be used on a payment network. If the site router is set to WPA3 only, or to a WPA2/WPA3 mixed mode that the device rejects, change the router to WPA2 before troubleshooting anything else.

Connect an XC23 or NextGen device

1. Go to the XC23 Home screen.
2. Tap the Settings icon.
3. Tap Network & internet.
4. Tap Wi-Fi.
5. Select the network the device will use.
6. Enter the password and tap Connect.

Connect a Verifone T650

1. Power the device on by holding the Power button on the left edge.
2. Wait a few minutes for the apps to load.
3. Once the Payments app is running, tap the Home button.
4. Swipe down from the top of the screen.
5. Press and hold the Wi-Fi icon in the top panel.
6. Select the network, enter the password and tap Connect.

Static IP over Ethernet on a Verifone T650

1. From the Home screen, swipe up.
2. Tap Settings, then Network and Internet, then Advanced Options.
3. Set Ethernet to Static.
4. Fill in the IP settings: IP Address, Gateway ID (the router default gateway), Network Prefix Length (default 24), DNS 1 (default 8.8.8.8) and DNS 2 (default 8.8.4.4).
5. Tap Save.

Use a static address for anything that other devices need to find reliably. Reserve the address on the router as well, so a DHCP lease does not hand it to something else.

Source: Global Payments Genius POS Setup Guide. Newly built article, pending review.