Field help (WEEKDAY)

Select this option in order to generate an invoice on a given weekday. The default value of the interval is 1.

It is considered that the week begins on Mondays and ends on Sundays. The reference invoice is considered to be the first recurring invoice. For instance:
Weekday = Friday,
Weekly interval = 1,
Accounting date of the reference invoice = Monday,
The next invoice will be generated Friday of the next week.

The field is available when the Weekly option is selected in the Recurrence pattern section.