For anyone running version prior to 5.4.0, there is an issue with Free coupons, here is the fix:
Edit the file src/addons/XFA/RMMarketplace/XFRM/Entity/ResourceItem.php
Search for:
Add before:
Edit the file src/addons/XFA/RMMarketplace/XFRM/Entity/ResourceItem.php
Search for:
PHP:
case 'discount':
$price = $price - $coupon->coupon_amount;
break;
Add before:
PHP:
case 'free':
$price = $price - $this->xfa_rmmp_amount;
break;