curl --request GET \
  --url https://api.kit.com/v4/subscribers/{id} \
  --header 'X-Kit-Api-Key: <api-key>'

{
  "subscriber": {
    "id": 319,
    "first_name": "Alice",
    "email_address": "alice@convertkit.dev",
    "state": "active",
    "created_at": "2023-02-17T11:43:55Z",
    "fields": {
      "category": "One"
    },
    "canceled_at": null
  }
}