This page covers a few common issues known with watch apps. If this page doesn't answer your questions, you can contact me at email@example.com
Many people have reported that updating their iOS and watchOS did the trick. You might be using an outdated version. Please try updating first. The current watchOS version is 5.1.2.
After updating, if it's not available to install by the iPhone's "Watch" app (it should be at the very bottom of the screen), try to restart both of your devices. Keep in mind that bluetooth has to be active to install the app on your Watch.
Click here for instructions on updating your iOS: https://support.apple.com/en-us/HT204204
Click here for instructions on updating your watchOS: https://support.apple.com/en-us/HT204641
Firstly, check if the Watch is connected to the iPhone: at the bottom of the Watch's screen you should see one to three dots. If those are moving/changing it means that the connection is live. If they are stuck, check if bluetooth is activated. Then, check if you have logged in correctly using the iPhone app. If the login button leads you to a preview of your home feed, it is working correctly. If that doesn't work, try to restart both of your devices. The last thing you can try is to uninstall and reinstall the app.
If your problems aren't answered, please contact me, I am happy to help!