When you add the GA4 client to a server container, GTM gives you a form with six fields and a vague hint about what they do. Three of them ship reasonable defaults. The other three are where the interesting decisions live.

Activation request path

Default is Default + Custom paths. Leave it. Custom paths only matter if you are running a non-standard endpoint, which most teams are not. If you are routing GA4 hits through a custom path for ad-blocker resilience, list the path here so the client picks them up.

Allow gtag custom domain

Turn this on. With it off, your client GTM still hits www.googletagmanager.com for the gtag config endpoint, defeating most of the point of running server-side. With it on, gtag config requests route through your custom tagging domain.

Default purchase currency

If your site sends currency on every purchase event (it should), this never fires. If it does not, GA4 falls back to the value here. Setting it to your dominant currency at least keeps the dashboard from showing values in mixed denominations.

The toggle most teams forget

There is a checkbox labelled "claim untrusted user properties." Off by default. Turn it on if your client-side code sets user properties via gtag('set', 'user_properties', ...) and you are seeing them dropped server-side. The default behaviour ignores user properties that did not originate inside the server container, which surprises everyone the first time.

A working baseline

For most setups, the right configuration is: default activation path, gtag custom domain enabled, default currency set, claim untrusted user properties enabled, log type set to "Always log to console" while you are debugging, and Cookie domain set to auto.

Once the client is wired up, the next decision is what to do about deduplication for the events you also send to Meta or TikTok.