I’ve recently implemented Google Tag Manager Server Side on a site that uses a 3rd party for checkout.

The checkout uses 2 domains outside of our control and not on the domains set to our GTM Server Side container. The approximate flow is:

1. User browses pages on our-domain.com and clicks to the checkout.
2. User starts the checkout process on 3rd-party-checkout.com .
3. User completes the purchase on 3rd-party-payment-gateway.com .
4. User is directed back to confirmation page back on 3rd-party-checkout.com.

Only our-domain.com is within our control and set to GTM Server Side.

When in Preview Mode on the client container I can see all events independent of domain being sent to the server container. Events originating on our-domain.com are visible in Server Side Preview Mode but no events are visible for the latter 2 domains.

Likewise those events from our-domain.com are visible in GA4, purchase events through the process are not visible if using server-side instrumentation, but are visible using client-side instrumentation.

Is there a way to ensure purchase events are visible using GTM Server Side given the above domain limitations?