Hi @dplavin, welcome to the community forum! We are deprecating the click-through service because it was just not supported or used by the community.
This API query - http://api.crossref.org/works?filter=has-license:true,has-full-text:true,license.version:tdm - will give you all the DOIs with a text and data mining license registered with us.
Please let me know if you have any additional questions.
Kind regards,
Isaac