Http post from keap campaign to create a gotowebinar registrant

Hi, I am trying to do a simple http post to create a gotowebinar registrant from a Keap campaign. I am not very technical but i’m the one who has to do it. I know where to do the http post from (the campaign SEND HTTP POST), i just need to know if this is possible and if so what POST URL to use and what Name / Value Pairs for first name, last name and email. I got the below from the gotowebinar API and i know my organiserkey and webinarkey but i still can’t get it to work. I know you can do this using Zapier, but thought there must be an easy way to do it directly from a simple Http post? Thanks for your help. Darren{organizerKey}/webinars/{webinarKey}/registrants

In order for this to work, you’ll first need to be sure certain values are stored in custom fields. specifically, you’ll need the organizerKey in a custom field and the webinarKey in a custom field. Then you can use those fields to merge those values where they are referenced. It would look something similar to the below: