curl --request POST \
  --url https://{cluster}.cognitedata.com/api/v1/projects/{project}/writeback/sap/instances \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "items": [
    {
      "externalId": "my.known.id",
      "gatewayUrl": "<string>",
      "client": 123,
      "username": "<string>",
      "password": "<string>"
    }
  ]
}
'

{
  "items": [
    {
      "externalId": "my.known.id",
      "gatewayUrl": "<string>",
      "client": 123,
      "createdTime": 1730204346000,
      "lastUpdatedTime": 1730204346000,
      "username": "<string>"
    }
  ]
}