Due to various reasons (such as Apple developer account termination), apps you had previously purchased can no longer be downloaded from the App Store or iTunes. However, it turns out these applications can still be accessed. Third party .ipa downloading tools such as iMazing, ipatool, and ipatool-py use a special endpoint that allows downloading removed apps.
This app must have been purchased on your Apple ID beforehand. You cannot download any app ever made. Apple only lets you download apps you had bought or downloaded in the past.
I reccomend using the ipatool-py method, because it is easier. However, if you are unable to use it, I have left the original iMazing method for you to follow.
- App ID (Number such as 1053533457) of app to download