Managing memberships in ActiveCampaign (or other CRMs)

We just launched a new Subscription/Membership service using Squarespace and Stripe for payments.

What’s the best way to manage these memberships outside of Squarespace?

I need to be able to manage our members-only mailing list effectively including subs, unsubs, and EDM’s. There isn't a Zap for this. So at the moment, I've just been manually copying them across every month. This creates obvious issues e.g. cancellations. 

Help!