curl --request PUT \
  --url https://api.serial.io/work-orders/{id}/approvals \
  --header 'Authorization: Bearer <token>'

{
  "approver_user_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "requested_by_user_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a"
}