How to insert a ZohoUser in a subform field?

How to insert a ZohoUser in a subform field?

I am building an new external web app that uses the ZohoCRM REST API (v8) to push data to Zoho. 
How do I use the ZohoCRM REST API to insert ZohoUsers into a subform field?  I've tried several approaches and none of them have worked - inserting the ID as a string, inserting an object with an "id" attribute.

Here's relevant information from my schema - 

Allocations (Custom Module)
- Sales_Order: lookup to Sales_Orders (just here so you can see how this relates to other Modules)
- Partner_Allocation: subform, Partner_Allocation

Partner_Allocation
- Parent_Id: lookup → lookup to "Allocations"
- Partner: lookup → lookup to "ZohoUsers"

And here my console log that includes the payload I am sending and the error I get when I try to PUT a new value.  This works correctly if I *don't* pass in a value for Partner, but I want to set this value. 

  1. [Zoho] PUT https://www.zohoapis.com/crm/v8/Allocations
  2. Payload: {"data":[{"id":"3062214000179868001","Partner_Allocation":[{"Open":100,"Close":100,"Delivery":100,"Partner":"3062214000006944015"},{"id":"3062214000179868002","_delete":null},{"id":"3062214000179868003","_delete":null}]}],"trigger":["workflow"]}
  3. Error updating allocation: Error: Zoho API error: 400 {"data":[{"code":"INVALID_DATA","details":{"api_name":"Partner","json_path":"$.data[0].Partner_Allocation[0].Partner"},"message":"invalid data","status":"error"}]}
  4.     at zohoRequest (lib/zoho.ts:155:12)
  5.     at async doTheUpsert (lib/services/SalesOrderService.ts:355:12)
  6.     at async createSalesOrder (lib/services/SalesOrderService.ts:369:6)
  7.     at async createEngagement (components/accounts/actions/engagements.ts:114:24)
  8.   153 |
  9.   154 |     if (!res.ok) {
  10. > 155 |       throw new Error(`Zoho API error: ${res.status} ${await res.text()}`)
  11.       |            ^
  12.   156 |     }
  13.   157 |
  14.   158 |     logRateLimitHeaders(res)

I get the ID that I am sending from the Users that come back from a `/users?type=AllUsers` call with a `Partner` role - 
  1. {
    "id": "3062214000006944015",
    "name": "",
    "email": "user@example.com",
    "role": {
    "name": "Partner",
    "id": "3062214000000026008"
    }
    },
Thanks for any guidance from the community!
Best,
-e