Can't link tag to Beeminder goal on Android

I'm a new user of the Android app, and have not been able to link any Beeminder goals to my tags. When I select a tag, my goal selection is unset; and when I select a goal, my tag selection is unset. And, of course, it won't let me save because one or the other is unset.

My phone is a Moto G5 Plus running Android 8.1.0. The version of the TagTime app I have is 1.3.4.