POST /customers

Unrecognised fields are refused. external_customer_id (≤200) and email required.
curl -X POST https://www.niftipay.com/api/v1/partner/customers \
  -H "Authorization: Bearer $PARTNER_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: <uuid>"
{
  "request_id": "req-1",
  "api_version": "2026-08-01",
  "data": {
    "partner_customer_id": "pc-1",
    "customer_id": "user_abc",
    "external_customer_id": "cust_42",
    "relationship_status": "active",
    "created_at": "2026-08-01T00:00:00.000Z",
    "customer": {
      "email": "buyer@example.com",
      "name": null,
      "country": null,
      "created_at": null
    }
  }
}