First, please double-check the code you are copying and pasting to ensure that you are using the entire code and haven't accidentally cut off part of the coupon code.
If it still does not work, please let us know what the code is that you're trying to use, so we can check to see whether it is valid.
We also recommend trying a different device or browser, or clearing your cache and cookies. And please remember that only one promotion can be applied per order, so if another offer was already applied, you will not be able to add another.