used property
Used is how many zero-priced calls this subject has been SERVED in the period ending at Resets — the UTC calendar day. Only a served call counts, so an admission check, a refusal, or a vendor that never answered leaves it where it stood. It stops AT Limit rather than climbing past it, so Limit-Used is what remains and never goes negative.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
int? used;