curl --request POST \
  --url https://api-m.sandbox.paypal.com/v1/customer/disputes/{id}/acknowledge-return-item \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: multipart/form-data' \
  --form acknowledgement_document=@example-file

{
  "links": [
    {
      "href": "<string>",
      "rel": "<string>",
      "method": "GET"
    }
  ]
}