jenbalco Based on my experience, setting up the "Send Form Data to Another Website" feature in Machform is inherently not easy. It requires a lot of time and a lot of trial and error. I was never very successful with it, so I suppose I shouldn't be offering any advice at all, but I wanted to mention that there is an example offered on the documentation portion of the Machform website of how to set up the "Send Form Data to Another Website" feature with Mailchimp.
I don't know if it will be useful to you at all (assuming that you haven't seen it already), but that's the only example for this feature that the Machform team provides. I hope someone else who has used this feature successfully will speak up with better information.