Is there a way of creating a referral link for community members to share with their friends to join a specific group? This would be a brilliant way to gamify adding people to your community...

So excited to join Skool and create my own community. Already loving the platform. I had a question. If I have a few people start off on a set fee of lets say $3 a month to join and decide to increase the price to $5 a month? Would they be charged $5 a month or would they remain at $3? I was hoping to only increase fee's to new members and keep the price the same for those who join early.