We currently have a discount code for Free shipping for any orders over $200 which is automatically applied at checkout.
However we also have some additional discount codes to offer $10 or $15 off, but these codes are set to not be used with any other promotions. If the customer adds these discount codes to checkout, it removes the free shipping offer and adds this code instead, however there is no error or message to say what has happened. The free shipping code is then lost and cannot be re-added.
Checkout should tell customers they cannot use the $10 or $15 code with other discount codes, and show that the Free shipping code is already applied. They can then decide to remove the free shipping if they want.
