Staying logged in, multiple domains

I want to remain logged in when going to a different subdomain.

This used to work by adding .domain1.app in my site security cookie options.
Then if I am on sub.domain1.app and switch to different.domain1.app it kept me logged in.

However I’ve recently added another domain, lets call it domain2.shop.

This is how I’ve got my cookie options set up (no idea if I can actually use a comma delimiter?)

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