Make sure you use iOS is 8.2 or later on your iPhone. Open the Watch app on your iPhone, select Buy Me a Pie! and set the “Show App on the Apple Watch” option to ON. As a result, you will see a small round icon of Buy Me a Pie! on your Apple Watch among the icons of the other apps:

There are two ways you can start Buy Me a Pie! on your Apple Watch:

  • tap the app icon;
  • swipe up from your watch face and tap the app Glance. Glances are scannable summaries of the information you seek out most frequently. Buy Me a Pie! Glance displays the number of products in the last list you’ve opened.

If you are not logged in to your account in the Buy Me a Pie! app, after launching the app on your Apple Watch it will ask you to log in on your iPhone first.

You can also add a complication for the Buy Me a Pie! app to make the icon show on the watch face.