Coupon only Payment

Mike,
This can be done as simple customization.
Do you need this for v3 or v4 ?

For v3 create file /amember/site.inc.php with this code:

PHP:

<?php 
setup_plugin_hook("validate_signup_form", 'vsf');
function vsf($vars){
  if($vars[product_id]==1 && !$vars[coupon]){
     $errors[] = "Product 1 can be purchased using coupon code only";
  }
  return $errors;
}
?>