AltE has a two part series that breaks down all you need to know about rapid shutdown and inverters and charge controllers. They cover the 2014 NEC requirements up to the most recent 2020 ones. The inverter article discusses the heartbeat keep alive and external communication options and the corresponding solutions while the charge controller article details solutions from Outback, Midnite, Schneider, and addresses compatibility issues. The visuals are very clear, potentially good for client discussions.