5
You have multiple options...
Debug the zencart stuff and the blank page... which is fun, but might be time consuming.
Also, hopefully, you have a development server you can try stuff on (like turning debug modus on)
The other option is to use XosC .73 Beta
(which was announced on the frontpage)
https://xoops.org/modules/news/article.php?storyid=3933
I'll help with the debugging, as others might help too...