The best way to pair your charger to your phone is via bluetooth. If you can't do this for any reason, or would like to pair a charger remotely, you can do so manually.
To do this, your charger has to be online. You can find out how to set up a Wi-Fi connection here.
Press the hamburger button (the three lines in the top left) to open the menu below and select Help & Feedback
The serial is your chargers serial number. Contact us for your API key.