Some publishers will require you to use the CrossRef click-through service. This allows you to agree to supplementary licenses. For more information see the Click-Through Service documentation. When you use the click-through service you will be given a token. You should supply this as a header when you make the query to full-text. Here is an example request using a click-through service token:
not sure what i was originally trying to say here, i guess just make sure to support click through as well as possible