How to use a custom date/time ticket attribute as ticket start date with Web Service Methods

Hi,

We're trying to use Web Service Methods to create ticket tasks (e.g. 'Deliver Furniture') whose start date/time is based on a ticket's custom date/time attribute (e.g. 'Delivery Time'). The end goal is remind our facilities staff to deliver furniture at a specific time, since the event/space booking ticket request is often submitted weeks before the delivery.  Having a task start date will allow us to send a timed reminder email and/or allow us to get it into a more user-friendly report or calendar view (ideally Outlook).

The web service is creating the task successfully, but I cannot figure out how to pass the 'Delivery Time' value over to the Web Service Method. Is this possible to achieve with a single Web Service step using 2 parameters, or should I be creating multiple methods to GET and PATCH this date/time information into the task?

What I've tried so far:

• POST​​​​​​​ with [Our URL]/TDWebApi/api/[Our ticketing app ID]/tickets/{{ticketId}}/tasks
• 2 Parameters:
  • ticketId (String from ticket ID)
  • start (UTC_DateTime from ticket custom date/time attribute 'Delivery Time') * I also tried String, and couldn't even pass it over as text in the Task Description
• Body:
  • {
    "Title":"Deliver Furniture",
    "StartDate":"{{start}}",
    "CompleteWithinMinutes":"60",
    }

Thanks,

Stephen