If user already logged in, Emerald action will still be triggered when he purchase a subscription

nican Will this be the case or the user always need to log-off and log-in again after purchase for the action to be triggered?

No. this is done in background seamlessly.

nican Another question would be about manually activated subscriptions: If I activate a subcription manually, actions will be triggered immediately? Or the user always need to log-off and log-in again?

He do not need to login or logoff. Actions will be tryggered before any next page of your site will be rendered.

nican P.S. I know I can use [PAID] tags to check user subscriptions instead that Joomla group, but it causes issues when I try to hide/show long or complex part of the code, I am using instead RegularLabs "Conditional Contents" tags, which seems to work without issues even when hiding/showing very long and complex html code... and "Conditional Contents" needs to check the user group.

Of course. in your case Groups change is the most convinient way to go. [PAID] is little bit more techy but more flexible in some cases.

That's great, thank you Sergey :)