American Airlines app no longer working on Apple Watch.

I’m using an Apple Watch 3 Edition, model A1861 running 5.1.3. Previously, my American Airlines app was syncing perfectly with the watch and I was able to view my itineraries, check

in, and bring up the mobile boarding pass on the watch to board flights. Currently, it’s no lot working and anytime I try to bring up the app on the watch, nothing happens. I need to know what to do to get it to work again. Thanks!