AddOn Domain Via URL/API or GET/POST

I can't seem to find the right information to be able to add a domain to my cPanel via either a URL/API or a GET/POST call. I've looked through the cPanel wiki and documentation, but it's all pretty 'confusing' for lack of a better word. Would somebody be so kind as to show me the proper format to add a domain to my cPanel account via either or both methods? Thanks so much! Jeff