There are some checks that need to be performed on the last day of the month, but no way to specify it in the interval.

May be is possible to espedify one letter, like L, to spedify last day of month

As a work arroud. it may be possible to specify 28,29,30 and 31 as day of month and discard the value if it is not the last day of the month but this will execute the item at leas 2 times every month, perhaps with some consecuences