Same issue here. I was logged in, but my subscription lapsed. I renewed, and now can't log into the iPhone app. I uninstalled the app, and clicked on the link to the app from here
http://www.thehighersidechatsplus.com/listening-faq to reinstall the app, but no dice. I've tried by username and my email address to log in, tried typing my password and having iOS auto populate the password after my thumb verification, and still getting failed to log in. The Plus shows used to be in the Podcast app, and you'd log in there, but I don't think that they are anymore.