The course is System Architect Essentials 7.3/7.4 and I'm at the "setting properties automatically" it says I should use author.hrapps / rules but those credentials don't work in the exercise system launched. The launched login page indicates the version is 7.3.1 at the bottom. https://paex54-use.pegacloud.io/prweb
The link you provided (https://paex54-use.pegacloud.io/prweb) isn't sufficient to access your specific environment. That system hosts multiple student environments, so the exercise credentials won't work on that screen.
If you click the Open Exercise System link on the exercise page, that will take you to the login screen for your dedicated environment. You can copy that URL or bookmark that page to return to the exercise system at a later time, but the URL needs to include the session identifier to access the correct exercise system.
Sorry for the delay. You should now be able to continue with your exercise. Please logout of Pega Academy, clear your browser cache, and login again. When you click on the "Open exercise system" link, you should now be able to login using author.hrapps, and continue from the "Initializing a page type property" exercise.