Why is sending calendar invites still this painful in 2025?

I’ve been building event-driven tools for years, and the same problem keeps coming up: sending calendar invites programmatically is still a mess. ICS is 25 years old, breaks differently across Gmail/Outlook/Apple, and handling updates + RSVPs reliably is harder than it should be. Not to mention the hidden limits enforced by Google Calendar via their API!

So I’m building Synara, a modern API for invites, RSVPs, and real-time event updates. Minimal use of ICS files, no calendar-provider weirdness, just consistent behaviour for developers.

If you’ve ever built anything involving booking, scheduling, or event syncing, I’d love to know: What was the single most annoying calendar-related issue you ran into?