Why can the guest checkout even though they are not allowed to make a purchase?

Hi, i purchased the pro version of the plugin. I will primarily use this plugin solely to limit purchase of Gift cards. Im using woocommerce gift card plugin however, there is a problem.

if you are a registered user, then, no issue – plugin successfully limits your purchase to 1 with an error message.

however, if you are a guest, even if guest are not allowed to purchase on the settings – they can still click ADD TO CART on the gift card and can still customize it for some unknown reason. There will even be a add to cart success message but in reality, product cannot be placed on the cart so after the customization of the gift card and checking out – they will checkout with an empty cart.

i hope someone can help me on this. I want the plugin to show and error message so that client will not waste time adding the gift card on their cart.