The account's current balance.

404. The resource is unknown or belongs to another marketplace; the response is identical
in both cases. Codes include ONBOARDING_NOT_FOUND, PROFILE_NOT_FOUND,
ACCOUNT_NOT_FOUND, TRANSFER_NOT_FOUND and TRANSFER_ACCOUNT_NOT_OWNED.

422. The resource is in a state that does not allow the operation, a submitted document
is invalid, or the idempotency key was reused with a different payload. Codes include
INVALID_STATE, INVALID_FIELD_FOR_PROFILE_TYPE, INVALID_PARAMETER,
INVALID_DOCUMENT, INVALID_ONBOARDING_DATA, DOCUMENT_ALREADY_REGISTERED,
MISSING_REQUIRED_DOCUMENTS, ONBOARDING_ALREADY_PROCESSING,
IDEMPOTENCY_PAYLOAD_MISMATCH, TRANSFER_DESTINATION_MISMATCH,
TRANSFER_ACCOUNT_NOT_VALIDATED, INVALID_OPERATION_TYPE, MALFORMED_REQUEST
and RESOURCE_BUSY.