Retrieve available cash balance across one or more currencies.
OAuth 2.0 bearer token issued by Wealthyhood. Include this token in the Authorization header
as Bearer <token>.
The bank's unique identifier for the acting customer. Must match the user associated with the bearer token.
"bank-user-12345"
Optional ISO 4217 currency code to filter results (e.g., USD, EUR, GBP). If omitted, returns all currencies.
"USD"
Cash balance response.