The Help Center 's Send a Request has a category specific for this: I have a bug to report about an official Roll20 Marketplace Item. When Roll20 closed down all the Bug Forum's WotC megathreads, there was a message for people to report all future marketplace issues using the Send a Request button.
This is a DMDave module, though, not an official Roll20/WotC one. I was going to DM DMDave, but the link in the Marketplace goes to the publisher page and that doesn't seem to have a way to message them directly...
I knew I had seen it somewhere, but took me a bit to find the thread. You might want to post here: <a href="https://app.roll20.net/forum/post/8835175/dmdave-bug-reporting" rel="nofollow">https://app.roll20.net/forum/post/8835175/dmdave-bug-reporting</a>