I thought I’d put this note here because while there’s some generic information on this topic from back in 2017, it still exists today in the latest version of GarageSale version 8.1.1. While the “verify listing” checks come back ok, when posting it, the HTTPS error comes back from the system and at first I didn’t know what was causing it. After all, I was using the latest version and wasn’t importing or using older templates or auctions. It turns out that the “Download URL” in the Image Server settings needs to be https://. This makes sense of course however it’s somewhat hard to find and could easily be overlooked. I actually typed my <domain.com/directory> leaving out the https:// altogether and it of course defaulted to http:// which triggered the error. Hopefully this helps someone else.