Chamberlain Internet Gateway connected to MyQ Garage Opener, but doesn't appear in app
I called up tech support this morning.

They told me that if the gateway said it was programmed (as indicated by a steady blue light), but the device wasn't appearing, it meant that I needed to reset the gateway.

Resetting the Gateway

The process for resetting the gateway is you disconnect it from power, then press the recessed button located on the long side above the logo sticker - I used a bent paperclip to do this. While still pressing the button, connect it to power.

Once you see the "yellow" (looked orange to me) light come on, you can release the button.

The device should now be reset. The green light will flash indicating that it's trying to get an internet connection. Eventually it should become solid (within ~20 seconds), indicating that it has its connection.

Adding the Device

Login to your account on your computer or phone again and tell it to add the device. Press the learn button on the motor and within ~5 seconds the main lightbulbs on the motor (not the smaller LEDs) should flash, indicating that the gateway has successfully been connected.

Check your account again and the device should now appear properly.

Hope this helps other people.