currency property
Currency is the ISO 4217 code Monthly is denominated in. Without it the number beside it means nothing, so the two are always read together.
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
String? currency;