Understood. Thanks for going through the troubleshooting steps with me, I'll have to get in touch with the Itch.io staff to figure out what might be causing the issue. This is my first time selling anything on Itch.io so its all new to me. It looks like most people have been able to get their key alright, based on conversations I've there is clearly something going wrong with your download page.
If you can send me an email to mercenarymarketplace@gmail.com from the email address you purchased the module with, I'll email you a copy of your key.