Chargify 

Chargify makes it easy to do subscription billing for web 2.0 and SaaS companies hassle free and PCI compliant.

This app is designed to make running your subscription based business a snap. They send the emails, help you take care of expired or declined cards, and most of all automatically charge your customers without you having to worry about it.

Using Chargify with ActiveCampaign will allow you to add new customers in Chargify to your Active Campaign lists and automations.