Cross Domain and server side tracking: Newbie questions

Hey everyone,

I’m a bit of a newbie here and was wondering if anyone can answer a few questions please?

I currently have UA and GA4 both set up with crossdomain tracking. (I have a blog that gets traffic, and run ads to, and then a product site that gets traffic from the blog and its own retargeting ads etc)

The UA is linked and a single site login etc and both sites tracking is installed via GTM.

I’m looking at setting up server side tracking right now for more accurate analytics and also to set up server side conversion tracking, however its a bit of a minefield to wrap my head around.

If I set up a subdomain for server tracking, will this work for both sites?
Or will I need a separate one for each site?

Sorry if this is obvious!


You can use one sGTM custom domain in case all your sites are at same main domain.
For example this will be valid: -- sGTM

In case you have different domains then you need separate custom domains fo sGTM
For example this will be not valid: -- sGTM