Approving pipeline stage in Azure Devops via API

I am trying to approve stages of a multi-stage yaml pipeline in azure devops but my REST requests to the endpoint detailed here return an error

{
  "$id": "1",
  "innerException": null,
  "message": "Value cannot be null.\r\nParameter name: updateParameters",
  "typeName": "System.ArgumentNullException, mscorlib",
  "typeKey": "ArgumentNullException",
  "errorCode": 0,
  "eventId": 0
}

I followed the strategy of obtaining the approval ID from the timeline of the pipeline (documented here), then getting the approval details (documented here), which gave me the 2 objects:

Approval stage from timeline

{
  "previousAttempts": [],
  "id": "e23aa595-7745-4015-9fdd-be7863faeda1",
  "parentId": "4ae2b754-452d-5a7c-1d05-4887a615523a",
  "type": "Checkpoint.Approval",
  "name": "Checkpoint.Approval",
  "startTime": "2023-11-15T12:36:50.5633333Z",
  "finishTime": null,
  "currentOperation": null,
  "percentComplete": null,
  "state": "inProgress",
  "result": null,
  "resultCode": null,
  "changeId": 71,
  "lastModified": "0001-01-01T00:00:00",
  "workerName": null,
  "details": null,
  "errorCount": 0,
  "warningCount": 0,
  "url": null,
  "log": null,
  "task": null,
  "attempt": 1,
  "identifier": "e23aa595-7745-4015-9fdd-be7863faeda1"
}

and approval direct from GET request

{
  "id": "e23aa595-7745-4015-9fdd-be7863faeda1",
  "steps": [],
  "status": "pending",
  "createdOn": "2023-11-15T12:36:50.53Z",
  "lastModifiedOn": "2023-11-15T12:36:50.531529Z",
  "executionOrder": "anyOrder",
  "minRequiredApprovers": 1,
  "blockedApprovers": [],
  "_links": {
    "self": {
      "href": "https://dev.azure.com/<orgName>/8f6c8014-5c15-49aa-8efc-adb274f30be3/_apis/pipelines/approvals/e23aa595-7745-4015-9fdd-be7863faeda1"
    }
  },
  "pipeline": {
    "owner": {
      "_links": "@{web=; self=}",
      "id": 23633,
      "name": "20231115.7"
    },
    "id": "64",
    "name": "Traveller"
  }
}

I then constructed the PATCH body

[
    {
        "status":  "approved",
        "approvalId":  "e23aa595-7745-4015-9fdd-be7863faeda1",
        "comment":  ""
    }
]

and sent this to the endpoint

https://dev.azure.com/<orgName>/<projectname>/_apis/pipelines/approvals?api-version=7.1-preview.

All documentation and other questions on this subject suggest I am doing this correctly, yet I cannot get past this error.

Other SO question consulted include this and this

I can reproduce the same issue.

The cause of the issue is that the format: $body | ConvertTo-Json will not add the [] in the request body.

To solve this issue, you can change to use the following format: ConvertTo-Json $body

$response = Invoke-RestMethod -Method PATCH -Uri  $uri -Headers $headers  -Body ( ConvertTo-Json $body  ) -ContentType "application/json"

Then it will pass the correct request body to the Request.