App Wrapper requires some system configuration before it can wrap applications. To see what needs to be set-up, select "Code Signing Diagnostics" from the "App Wrapper" menu. Please note that this may only take a brief second, or it may take several.
Once the "Code Signing Diagnostics" report has been generated, it should look something like below.
Currently you need to be running macOS 10.13.6 or newer in order to submit applications to Apple. If not please consider running a newer version in a VM machine, so it doesn't damage your workflow.
To submit apps to Apple, Xcode 10 or newer must be installed and configured. If any of the tools are missing or there are Xcode issues, Read Tool Issues
To distribute applications over your own website, you need to have at least one account with "Developer ID Application" and "Developer ID Installer" certificates installed. Read Managing Certificates for information on how to download or replace certificates. These require a paid subscript to Apple's Developer program.
To distribute applications through the App Store, you need to have at least one account with "Apple Distribution" and "3rd Party Mac Developer Installer" certificates installed. Read Managing Certificates for information on how to download or replace certificates. These require a paid subscript to Apple's Developer program.