Get account balance

Return the current BRL balance for the company associated with the API key. The endpoint takes no parameters — the company is always derived from the API key. The four balance buckets are independent and additive: available (settled funds free to use; a withdrawal is also bounded by GET /v1/withdrawals/limits), frozen (set aside for in-flight withdrawals, refunds, or operational holds — not currently withdrawable), held (confirmed but pending settlement), and reserved (a rolling reserve withheld from settled funds and released on a schedule — not currently withdrawable). The total account balance is available + frozen + held + reserved. A split credit received from another YuvexPay company follows your own rolling reserve policy, not the originating company's. A sandbox API key always returns zeros, since sandbox transactions do not accumulate to a real balance.