Coupon codes cannot be used alongside the Buy One Get One Free Wishful promotion (with the exception of coupon codes issued in redemption of loyalty points).
If you have a valid coupon code, it should apply to other full price items on your basket that is not a Wishful product or part of the promotion. Alternatively, you can save your code to redeem on your next order.
If you use a coupon code that has been issued in exchange of your loyalty points, it will be valid with this promotion, and you should see the discount apply at checkout.