Fix a little issue on Magento 1.9

Hello I have a Magento store (v1.9.2.4) and I'm facing a little issue that will be easy to resolve for who has experience Basically, I installed a module for affiliates which I want to work with affiliates coupons, but the problem is not exactly on this module. The issue is that in my coupon field on the checkout page, the coupon doesn't work. (Just the affiliate module coupon, the native Magento coupon works fine), but it works well on the native coupon field on the cart page. The job will be basically find what is the difference between the coupon field on the checkout page, and on the cart page, what makes the coupon works on the cart page and replicate this on the checkout page to get working there too. That's all