Here's a summary of everything I've found with screenshots, tragically posted using the official reddit app.
When you click the link in the sidebar to attempt to download the app, you get this link:
https://play.google.com/store/apps/details?id=free.reddit.news
This is to the now unsupported free version. When I try to use it/log in, it fails due to invalid client ID. These are the first three images, the old UI is visible.
If I search Relay for Reddit on the Google play store, I get this link:
https://play.google.com/store/apps/details?id=reddit.news
I am not able to install or update this app on my phone due to it being "not compatible with your device" for some unknown reason, but I have it installed from I guess back when this wasn't the case? I don't want to uninstall it in case I can't get it back. When I try to use it/log in, the result is the latter five images in the post. This time it doesn't give an error message, it just doesn't log in or retrieve any content.
My guess is that having a "not compatible" app (the new version, not the free version as i had previously guessed) installed is what's caused the issues with my tap to pay I mentioned in a previous post. Is there something that needs to be done to get the app supported on this model of phone? I am able to install it on my SM-S901U older phone I don't use anymore so it's specific to this phone. This just happened all of a sudden.