If we use a Hikashop coupon, the payment section does not display when the cart toal is $0.00. The Hikashop devs took a look and this is what they said -
I see what's going on. The issue is that you're using AWOCoupon and not HikaShop coupons.
And apparently, the way they add the coupons to the cart is too late in the cart loading process for HikaShop's payment method system to know that the price is 0.
Basically, the payment method system in HikaShop sees the price before the coupon is applied and thus it doesn't work properly.
I suppose that they must be using a trigger instead of another.
I would recommend them to implement the trigger onAfterCartShippingLoad to add their coupon to the cart after the shipping is loaded, but before the payment is loaded. If they use the trigger onAfterFullCartLoad, the payment is already loaded when they add the coupon. It's still possible, but in that case, they have to unload the payment in the cart themselves when the total is 0.
Basically, I would recommend to contact AWOCoupon about that issue and provide them with this message. That should help them understand what needs to be done for the coupon to work properly with the payment methods during the checkout.
Can you check this out? It's causing issues with our cart and the ability to use gift certificates.