I have the same problem. I try logging into the app with credentials that DO work on browsers. I get sent a security code and enter it, then see the error message about my login or password being incorrect. This happens over and over again after countless attempts, after deleting and reinstalling the app, and selecting a different default browser (since the login seems to have some relation to that). I have reset my password repeatedly. Nothing has made a difference.
I get around this by using the internet version of the app but it would be nice to have the app’s features, such as appointment notifications.
I have not seen any solutions or hacks on the web, nor any company response to this issue.
I am on an iPhone, iOS 14.5.1.