Initiate a payment

curl -X POST "https://api.live.paisr.tech/v2/payments" \
  -H "Authorization: Bearer <access_token>" \
  -H "User-Agent: MyApp/1.0" \
  -H "Content-Type: application/json" \
  -d '{
  "invoice_id": "inv_123",
  "payment_method": {
    "type": "qr",
    "data": {
      "provider": "uni5pay"
    }
  },
  "billing_details": null
}'

{
  "success": true,
  "data": {
    "id": "pmt_123456",
    "status": "pending",
    "next_action": {
      "type": "present_or_trigger",
      "provider": "string",
      "qr_code": "string",
      "deep_link": "string"
    }
  }
}