Getting third party API code to work

I have built a contact form in webflow and trying to integrate it to a new lead api over in a system called Tave. I have put Tave’s endpoint into the webhooks settings and have custom PHP code from Tav and I’m unsure where it has to be placed for the integration to work. All my tests keep failing so I’m not sure what I am missing to get it working. I also experimented with Zapier and that errored too but would prefer not to use Zapier as there is clearly an integration that does work. Any help would be greatly appreciated!!!

Also - this is what the Tave site says: This is the class that is used to consume this webservice. In the constructor you specify your Studio Alias (mentioned above) and your API Key (mentioned above). Then just pass in the fields you want to send to the API, in the createLead method.

Here is my site Read-Only: Webflow - Vineyard Vibes