Unfortunately, iOS 13 broke compatibility with legacy versions of our apps. End of support for these apps was announced in January, 2018 and they were removed from sale on the App Store in July, 2018. At that time (when iOS 11 was current), we could not have known that Apple would break them in iOS 13.
Please understand that the apps you purchased still work just fine on the versions of iOS they were developed for and you can continue to run them on compatible devices.
If you have a device running iOS 12 or earlier, you can re-download the original app you purchased from your App Store account.
https://support.apple.com/en-us/HT201272
If you need to always be able to run SignalScope on the newest versions of iOS, we recommend that you download SignalScope X and choose a subscription option that best meets your needs (the Advanced Tool Set most closely matches the functionality of the old SignalScope Pro).
In case you prefer to avoid subscriptions, we still offer new
perpetual license versions of our products for those who need them (with the understanding that they will also be retired and replaced at some point, as the old apps were).
Unfortunately, since our app distribution must go through the App Store, we cannot offer discounted upgrades for purchases of our earlier apps, which is largely why we moved to a subscription model for our software.
A note about SignalScope X's auto-renewable subscriptions