Like mentioned in the email you received, your app writes to a directory which is not allowed. Sure, it happens because you followed the instructions in the sailjail repository. But the Sailjail stuff is not yet ready to be used by third party applications.
Might be so. Or not. I don’t know, and quite likely nobody does. That’s exactly why this stuff is not yet allowed in Harbour.
But anyway, thanks for testing the stuff, even if it’s not yet ready! The issue that you found is definitely one that needs to be sorted out sooner or later. Either by changing the Harbour rules, or by changing the Sailjail instructions.