Pin Activity Via REST API (Row Context?)

I am trying to pin an Activity to a Lead via REST API. There isn’t an action for togglePinActivity on the DEFAULT Lead endpoint out-of-the-box, so I added one:

I found a lead in the sales demo data that had multiple activities associated (Darren Walker):

I got into the DAC Schema browser and found the Note ID for the 3rd activity here (Summary: Follow up on pricing) and used that and the lead’s id (9833) to create an API request.

I POSTed to http://localhost/25R2SalesDemo/entity/ActivityPin/25.200.001/Lead/togglePinActivity

{
   "entity": {
    "LeadID":{"value":9833}
   },
   "parameters": {
    "id":"4d1a3b2c-d87f-e411-beca-00b56d0561c2",
    "NoteID":{"value":"4d1a3b2c-d87f-e411-beca-00b56d0561c2"}
    }
}

I tried the activity note two ways (id and NoteID). I get a 204, which is a successful response. I check the UI, and it did pin an activity, but always the first one, regardless of the ID parameter I send:

Posting again removes the pin on the first activity. How can I tell the API which activity I want it to act on? Am I structuring the parameters wrong? How do I even find out what parameters an action expects?