curl https://api.thanxsandbox.com/partner/campaigns/camp_abc123 \
  -X GET \
  -H 'X-ClientId: {client_id}' \
  -H 'Accept-Version: v4.0' \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer {access_token}'

{
  "campaign": {
    "id": "camp_abc123",
    "name": "Summer Free Coffee",
    "objective": "Re-engage lapsed customers",
    "start_at": "2025-06-01T00:00:00Z",
    "end_at": "2025-08-31T23:59:59Z",
    "redeemable_from": "2025-06-01T00:00:00Z",
    "redeemable_to": "2025-09-30T23:59:59Z",
    "time_zone": "America/Los_Angeles",
    "fine_print": "Limit one per customer",
    "variants": [
      {
        "id": "var_treat1",
        "name": "Treatment",
        "reward_template_id": "abc123def456"
      },
      {
        "id": "var_ctrl1",
        "name": "Control",
        "reward_template_id": null
      }
    ]
  }
}