Web Service Post string parameter is being passed with plusses instead of spaces

I have a Web Service Method that is Posting to the tickets endpoint to create a ticket in another ticketing application.

In the header, Content-type is being set to text/json.

There are parameters set to hold an integer for ticket ID, and string parameters to hold a textarea (A/V setup description) and checklist (equipment needed). 

The body contains:

{
"TypeID":"1138",
"FormID":"2639",
"Title":"A/V Request from Fac Tix: {{OrigTicketTitle}}",
"Description":"Created from Facilities Ticket {{OrigTicketID}} \n Equipment Needed: {{OrigTicketEquipment}} \n Details: {{OrigTicketAVDetails}}",
"AccountID": "{{OrigTicketAcct}}",
"SourceID": "354",
"StatusID": "773",
"PriorityID": "{{OrigTicketPriority}}",
"RequestorUID":"{{OrigTicketRequestorUID}}",
"Attributes":
  [
    { "Name": "Set-up Date", "ID": "5732", "Value": "{{OrigTicketAVSetup}}" },
    { "Name": "Tear-down Date and Time", "ID": "5733", "Value": "{{OrigTicketAVRemoval}}" }
  ]
}

The ticket that it created contains the following value in it's Description:

Created from Facilities Ticket 446269
Equipment Needed: Portable+Sound+System%2C+IT+Laptop+Check-Out
Details: set+up+details+go+here

Any suggestions on how to *not* have plus signs in between the words in the equipment list and the setup details?