ServiceDesk Plus Cloud API - upload file attachments using MS Power Automate

Hello,

I am using MS Power Automate ("PA") to upload file attachments from Sharepoint to a ServiceDesk request via the API. I am getting a response from the API that I am not understanding. The response is:

{
  "response_status": {
    "status_code": 4000,
    "messages": [
      {
        "status_code": 4001,
        "field": "file_list",
        "type": "failed"
      }
    ],
    "status": "failed"
  }
}

I have tested using a standalone python script and it was successful. My suspicion is there is a problem with the way PA is inserting the binary file data into the http request body.

Can someone shed some light on what that error might mean? I thought it might be a missing field in the request body, but the field "file_list' is not documented in the API documentation: https://www.manageengine.com/products/service-desk/sdpod-v3-api/requests/request.html#add-attachment-to-a-request

Headers are:

{
  "Content-Type": "multipart/form-data; boundary=<boundary>",
  "Accept": "application/vnd.manageengine.sdp.v3+json",
  "Authorization": "*sanitized*"
}

Body is:

--<boundary>\r\n

Content-Disposition: form-data; name="addtoattachment"\r\n\r\n

true\r\n

--<boundary>\r\n

Content-Disposition: form-data; name="filename"; filename="filename.png"\r\n

Content-Type: application/octet-stream\r\n\r\n

--<boundary>--