Callback url not called

[raquelhortab]

Hi, it seems like no one read this but I'll try anyway. I cant get the callback url to get called when a payment is completed. I am using the sandbox environment. I get to create the order and redirect the user to the payment page. The "back" button (success url) and the cancel url work. However, the callback url is never called. These are the main parts of the code:

order = CoinGate::Merchant::Order.create(
...
callback_url:         gift_card_confirmation_url(token: gift_card.key)
...
)

on routes.rb

post 'gift_cards/confirm_payment', to:'api/gift_cards#confirm_payment', as: :gift_card_confirmation

Can anyone point me out what is wrong?