Worth noting: There is no reason to send an eventsub everymonth for a multi month sub, as there isn’t a topic that does that.
Event sub broadcasts when a sub starts and ends and when it’s shared in chat.
So a multi month will trigger when it starts, when it ends and when a user shares in chat.
All resubs if not shared in chat trigger nothing on a monthly basis. There currently isn’t a “this sub is still running” message. UserVoice for that is here: Please provide an event sub that emits "resub payments" – Twitch UserVoice however that logically won’t trigger for a month in a multi month sub as no payment has occured.
However you can request additions to eventsub via uservoice:
https://twitch.uservoice.com/forums/310213-developers?category_id=396520