fieldNameStringRequired
The identifier used when reading or writing a value for this extra field.
labelNameStringRequired
The label to display for the extra field.
isRequiredBooleanRequired
Whether a value for this extra field is required.
visibleToEndUserBooleanRequired
Whether the merchant has made this extra field visible to storefront shoppers.
defaultNumberDoubleOptional
The value applied when the shopper supplies none.
maxValueDoubleOptional
The largest value allowed, or null if unbounded.
