Wallet Top-up.

POST /api/v1/wallet/pay/ loads money into the authenticated user's wallet using a saved card. amount is required (minimum 10, maximum 100000, up to 2 decimal places). card_id is optional; if omitted, the default card is used.

{
  "amount": 25.00,
  "card_id": "string"
}

{
  "success_message": "Payment successful for 25.00",
  "data": {
    "reference_id": "string",
    "amount": "25.00"
  },
  "success": true
}