The Unable to Verify App message usually means iOS cannot validate the certificate used to sign a sideloaded app such as ESign, KSign, or Scarlet.
For current installers, certificates, and iOS sideloading tools, visit the AppleJr iOS IPA Installer. If you use Scarlet, you can also check the Scarlet iOS installation page.
First, check whether the certificate used to install the app is still working. If the certificate has expired or been revoked, the same installation may stop opening or show an Unable to Verify App message.
In that situation, reinstalling the app with the same invalid certificate usually will not solve the problem. Use a currently valid certificate or signing method instead.
Open Settings → General → VPN & Device Management. If a developer profile for the installed app appears there, make sure it is trusted before opening the app again.
If the certificate is currently valid but the app still cannot be verified, remove the affected app and install it again. This can refresh the installed profile and signing information associated with the app.
If your installation method uses AppleJr DNS, confirm that the DNS profile is installed and active before reinstalling ESign, KSign, or Scarlet.
DNS can be part of the installation method, but it cannot turn an already expired or revoked certificate into a valid certificate. If the signing certificate is no longer valid, use another currently working certificate.
Normally, Erase All Content and Settings should not be your first solution. A factory reset does not make an expired or revoked signing certificate valid again. Only consider resetting the device for broader iOS problems after backing up your data and after simpler troubleshooting has failed.
You can follow the full tutorial in my YouTube video below:
This article is part of AppleJr Post.