It is part of the Payload of the webhook call - the syntax is below.
{
"salesOrg": "{{lead.Sales Org:default=edit me}}",
"contactId": "{{member.PMCFstring6}}",
"accountId": "{{lead.Account Nbr (SFDC):default=edit me}}",
"campaignName": "{{member.PMCFstring5}}",
"firstName": "{{lead.First Name:default=edit me}}",
"lastName": "{{lead.Last Name:default=edit me}}",
"fullName": "{{lead.Full Name:default=edit me}}",
"email": "{{lead.Email Address:default=edit me}}",
"phone": "{{lead.Phone Number:default=edit me}}",
"city": "{{lead.City:default=edit me}}",
"state": "{{lead.State:default=edit me}}",
"zip": "{{lead.Postal Code:default=edit me}}",
"country": "{{lead.Country:default=edit me}}",
"currencyIsoCode": "{{lead.Lead Currency:default=edit me}}",
"company": "{{lead.Company_formUse:default=edit me}}",
"profession": "{{lead.Profession:default=edit me}}",
"position": "{{lead.Primary Position:default=edit me}}",
"leadId": "{{member.PMCFstring7}}",
"products": "{{Lead.Web product Interest:default=edit me}}",
"inquiryType": "{{member.PMCFstring1}}",
"message": "{{Lead.Feedback_txt_long:default=edit me}}",
"formId": "{{member.PMCFstring3}}",
"formName": "{{member.PMCFstring4}}",
"formUrl": "{{member.PMCFstring2}}",
"sourceSystem": "{{lead.Lead Source:default=edit me}}"
}
The fields on the left are SFDC fields.
You don’t add quotes around the tokens in the payload.
JSON encoding takes care of quoting when necessary. It encodes values based on the datatype (string, number, boolean).