The most common cause on iPhone is the in-app browser. If a user clicked your Add to Calendar link from within Instagram, Facebook, or another social app, they're in a sandboxed browser that can't access the Calendar app. Ask them to open the link in Safari.

Full troubleshooting list for iPhone

1. In-app browser (most common) Social media apps open links in their own built-in browser, which has limited device access. The Add to Calendar flow requires access to the Calendar app or the ability to download an .ics file - both are restricted in in-app browsers. Fix: tap the "Open in Safari" option (usually a button in the bottom toolbar of the in-app browser).

2. iCloud Calendar not set as default When a user taps "Apple Calendar" in AddEvent's calendar picker, iOS opens the default calendar app. If iCloud is disabled or a third-party calendar app is set as default, the event may fail silently. Fix: Settings → Calendar → Default Calendar → select an iCloud calendar.

3. Safari pop-up blocker Some AddEvent flows open a new tab. If Safari's pop-up blocker is active, it prevents this. Fix: Settings → Safari → Block Pop-ups → turn off.

4. Older iOS version iOS versions below 14 handle .ics file downloads differently and may not open them in Calendar automatically. Fix: update to the latest iOS version.

5. The .ics file download fallback If the direct calendar flow doesn't work, the user can tap "Download .ics" in AddEvent's calendar picker. The file downloads to Files, and tapping it from there opens a Calendar import dialog on iOS - a reliable fallback for any iPhone issue.