Problem - Gift Card order's invoice is empty

Solution

Make sure the currency for the Generic Gift Card product is enabled for the user that is ordering the card.

If it is enabled, insert the following in your WHMCS configuration.php and run the checkout again.

$display_errors = true

Problem - Cannot Checkout 

Solution

Make sure the Payment Gateway for the Generic Product group is enabled for the Payment Gateway to use in the module's configuration

If it is enabled, insert the following in your WHMCS configuration.php and run the checkout again.

$display_errors = true