You may only have your terminal connected to POS or Billing Manager - they cannot be online simultaneously.
How to Plug Reader into Power
Slide off the bottom cover on the reader.
Plug the connector cable into the port and slide the cover back on.
Plug the power adapter into the connector cable and a power outlet.
Wait for it to boot, which may take several minutes.
Leaving the device on for extended periods is expected. Unplug it to turn it off if needed.
Connect Reader to Internet
You must connect your Verifone card reader to your local network to use it. This can be done via WiFi or an ethernet cable.
Connect via WiFi
Connecting over WiFi is a beta feature. For production use, have an Ethernet connection ready as a backup in case of degraded networks or connectivity issues.
Your WiFi network must use WPA-Personal or WPA2-Personal encryption and be password protected. WiFi is not supported for non-password-protected networks or enterprise networks.
If you’re setting up a new device, follow the on-screen prompts to connect to the internet using WiFi. To start over, press the red X button on the keypad.
To switch networks or connect an already online reader to a WiFi network, press 0WIFI (09434) on the keypad and follow the prompts.
Attempting to join a new network disconnects the reader from any existing wireless connection. There is no fallback to the previously connected network.
Connect via Ethernet Cable
Plug an ethernet cable from your router into the ETH port on the reader's connector cable.
The reader will attempt to connect with Stripe and may update itself.
How to Add Reader/Process a Payment
Enter 07139 into the terminal to display a registration code.
If using the card reader for both PoS and Billing manager, write down this code each time you switch between the two.
On your computer, navigate to your website and Sign In.
In the side menu, click Business Tools > Billing Manager.
Find the account you'd like to process a payment for. Click on their name.
Click on Payments...
Click Payment Methods > Credit Card.
Click Start Credit Card Payment.
Click Add New Reader...
Enter the reader's registration code from step 1.
Enter a Label, such as "Front Desk."
You can now select the card reader from the drop-down and click Start to process the payment.
Additional Resources: Verifone P400 Setup documentation