Tend app is no longer available in Apple App Store

I just purchased a new iPhone and the Tend app did not transition with my other apps.  When I attempted to download it again, it is no longer available in the app store.  However, I have been able to access my Stuart Minion cameras using the following website: app.isecurityplus.com using my old Tend app credentials.  Is anyone else having this issue.  The Tend app seems to still work fine on my other devices that have it previously installed.