Why are you forcing singup? Skip that, make it optional. When people are invited to an event send them a unique link tied to their email/phone number/WhatsApp or whatever. Create a long lived cookie that identifies them as that user. If someone really wants to create an account with a login and password let them, but don’t make them create yet another account to manage.
Edit: Also as you build the graph out, consider making all events private by default, and providing a what’s up feature that would let your friends/clique/circle/squad or whatever you are calling it know you are looking for plans tonight. Then let them opt you into visibility for their evening plans.