curl --request POST \
  --url https://api.recallrai.com/api/v1/users \
  --header 'Content-Type: application/json' \
  --header 'X-Recallr-Api-Key: <x-recallr-api-key>' \
  --header 'X-Recallr-Project-Id: <x-recallr-project-id>' \
  --data '
{
  "custom_user_id": "<string>",
  "metadata": {}
}
'

{
  "user": {
    "custom_user_id": "<string>",
    "metadata": {},
    "created_at": "2023-11-07T05:31:56Z",
    "last_active_at": "2023-11-07T05:31:56Z"
  }
}