Posting to a Custom Multi-select Field via Webhook using value from a Custom Text Entry Field

I'm looking to pull data out of a ticket description to auto-populate a multi-select field. I've already set up a trigger than can pull that data out, but I'm having trouble with inserting it into the custom multi-select field. 

To help, I broke the process into two parts and am first inserting those values into a custom text field. That part is working. I'm then trying to post that text field value as an array into the multi-select field and that has not yet been successful.

Here's the JSON that I'm currently using for the second step:

{
  "ticket": {
    "custom_fields": [{"id": 13597373709460,"value": "[{{ticket.ticket_field_16564070922516}}]"}],
  "comment": {
   "body": "[{{ticket.ticket_field_16564070922516}}]",
   "public": false}
    }
}

The custom multi-select field is ID 13597373709460 and the source custom text field is ID 16564070922516. I added a comment as well to verify that the trigger is firing. Any suggestions on how I can modify this to work?