How can Charts display sales data for a full month and support monthly paging?

Due to the varying number of days in each month, I am unsure how to enable monthly paging in Charts.

In Apple's official example, SwiftChartsExample, there is only an example showing the sales of the "last 30 days":

.chartXVisibleDomain(length: 3600 * 24 * 30)

I have tried using scrollPosition to calculate the number of days in the current month, like this:

var days: Int {
    let current = Calendar.current
    let dateRange = current.range(of: .day, in: .month, for: scrollPosition)
    return dateRange?.count ?? 0
}
...
.chartXVisibleDomain(length: 3600 * 24 * days)
...
.chartScrollPosition(x: $scrollPosition)
...

But I found that it does not work as expected. 😢