Share calendar for a group that uses WhatsApp to communicate

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A small club. We have a FB group but it's not used much now, with most members preferring to use the WhatsApp group.

It has been suggested we need a shared calendar to keep track of events. Ideally one that members can all add events to.

What would you use/how would you do it?

If they are all on iPhones, I would use a shared Apple calendar, if some are on Android, I would use google Calendar for everyone.

There'll be a mixture. C. 150 people.