Scott Have you checked the recent reviews of this app on https://play.google.com/store/apps/details?id=it.candy.simplyfi It seems that there is quite a few 1 star reviews saying the app doesn't really work.
Suggest trying these step by step instructions to see if they may resolve your issue.
FYI: Front-end clients, such as the AuroraStore, may be problematic, see here.
Side note, I don't know what kind of sign-in or how this app works, but something to keep in mind is this specific paragraph in the installation sub-section of our sandboxed google play usage guide:
Signing in into a Google account is optional, unless you want to use features depending on being signed into an account. For example, some apps use Google account authentication instead of their accounts having a username and password. The Play Store requires being signed into an account in order to install apps or use in-app purchases. This is still true even for an alternate frontend to the Play Store. Aurora Store still requires an account but fetches shared account credentials from Aurora Store's service by default.