const options = {method: 'GET', headers: {'x-api-key': '<api-key>'}};

fetch('https://sandboxapi.me-cash.com/v1/wallet/{walletId}/balance', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "message": "wallet balance fetched successfully",
  "status": "success",
  "data": {
    "id": "cfd2de64-a896-4405-8736-a1b2c3d4e5f6",
    "balance": 23094071,
    "currency": "NGN",
    "country": "NG"
  }
}