Photo 365 APP

I recently upgraded my IOS AND ALSO MY IPHONE TO THE 11. I have an app that I've had fro around 9 years called Photo365 I've used it to keep a daily log by photos. The program pics are uploaded to the cloud so anytime I upgraded it just downloaded back to my new phone. Now after I resore from backup I get a response of

Unable to install Photo365-Everyday photo calendar for your life.

This app is no longer available in the app store.

Does anyone know of anyway to get the app working? I have a lot of stuff on there that I would prefer not to loose.