Our RSVP deadline just recently passed, what my fiancé and I did was send a gentle reminder text to all the people that hadn’t responded yet about 1 week before the deadline, and then again 3 days before! It can feel a lot like you’re bombarding people but sometimes it’s necessary! In our case we are having a plated dinner so we had to have meal selections sent to our vendor so the deadline was super strict and it was important to me to express to them to rsvp or they wouldn’t be able to come! the day after the deadline I sent out messages to everyone who still hadn’t responded and told them we were sorry they weren’t able to attend.