Create an ics file
$ touch pay_day.ics
BEGIN:VCALENDAR
BEGIN:VEVENT
DTSTART;VALUE=DATE:20201215
DTEND;VALUE=DATE:20201215
RRULE:FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYMONTHDAY=15,-1
DESCRIPTION:
LOCATION:
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:Pay Day
TRANSP:TRANSPARENT
END:VEVENT
END:VCALENDAR