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

{
  "campaigns": [
    {
      "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
        }
      ]
    }
  ],
  "pagination": {
    "current_page": 1,
    "per_page": 10,
    "total_pages": 1
  }
}