Add referring agent

Adds a referring agent to the listing.

Validation & Requirements

Required Parameters

• listingGuid (path, string, format=guid)
• form (body, object)

Required JSON Body Fields

• None

Validations

• Invalid GUID values in *Guid/*Guids fields return 422 Unprocessable Entity.
• Invalid date values in *date* fields return 422 Unprocessable Entity.
• Missing required request body returns 422 Unprocessable Entity with Missing request body..
• Additional business-rule validation may return 422 with details in the errors array.
• If provided, email must be valid.
• Phone, fax, and alternate phone must be exactly 10 numeric digits.

Integration Requirement

• Retrieve the corresponding ...Form endpoint immediately before write operations to get current dynamic required fields and allowed values.