Our marketplace is a gateway between you and the developer. We can’t make business decisions for our Marketplace Providers like making the plugin free.
I think the more important issue here is that the developer does not claim to support HTML5. I took this screenshot from the documentation page.
https://develephant.github.io/coronium-core-docs/
If you feel that this is a deal breaker for you, we do have a process listed on our FAQ and EULA to request a refund:
How do I request a refund on a product?
As outlined in our Corona Marketplace EULA Sections 4.5 and 4.6, our refund policy is no refunds after 30 days from purchase date. You may request a refund within 30 days of purchase if the product hasn’t been downloaded or used yet. You may also request for a refund within the 30 days of purchase if there is an issue with the product that the Vendor fails to respond to your request to resolve the issue within 2 weeks. Once these conditions are met, you can contact support@coronalabs.com and we will help process your refund.
There’s a problem with the product I bought.
First try contacting the Vendor for any support related to the product you purchased. Different ways to reach the Vendor should be listed in the Vendor’s Profile page or the product’s page itself. If the Vendor fails to respond to your request to resolve the issue after 2 weeks and if the issue appears valid, please contact support@coronalabs.com to petition for a refund.
Reading those FAQ questions, if you’re past 30 days, there isn’t much we can do, but given you’re trying to use it on a platform that the vendor doesn’t claim to support, I’m not sure what recourse we have.
Rob