Upgrade from RW5 to RW6 - stacks missing

Hi. I have just upgraded from RW5 to RW6 on my Mac running El Capitan. When I open a website using RW6 I get a message saying that Stacks are missing and I won’t be able to publish. RW5 still works fine. I’ve tried in RW6 managing add-ons but can’t add the ordinary stacks and the ones I have purchased as extras. Help!

The stacks plugin has two different version, one for RapidWeaver 5 and one for RapidWeaver 6, sounds like you need to get the one for RapidWeaver 6