Store setup:
— Storefront: domain.com (BigCommerce Catalyst)
— Checkout: checkout.domain.com (BC-hosted checkout, no custom JS access)
Problem:
Because our store runs on Catalyst, BigCommerce routes checkout to a separate subdomain (checkout.domain.com). We have no ability to inject custom JavaScript or GTM tags on this checkout subdomain as it is fully managed by BigCommerce.
Klaviyo tracks users via the __kla_id cookie, which is scoped per subdomain. This means a user browsing domain.com gets one __kla_id (e.g. cid: "ZTY2MT...") and the same user on checkout.domain.com gets a completely different __kla_id (e.g. cid: "YmNjY2..."). These are treated as two separate anonymous profiles in Klaviyo.
For anonymous users (not yet identified, no $exchange_id in cookie), there is no way to pass the _kx parameter to the checkout URL to bridge identity, because _kx only works for already-identified users who have previously clicked a Klaviyo email.
This means:
1. Custom Klaviyo events fired on the main storefront (via GTM) are linked to one anonymous profile.
2. The "Started Checkout" event fired by BC's native Klaviyo integration on the checkout subdomain is linked to a completely different profile — even when the same user triggered both.
3. There is no way for us to set or share cookies across these two subdomains from the client side due to browser Same Origin Policy.
4. We have no server-side hook or custom code injection point on the BC-hosted checkout subdomain.
Question:
Is there a way for BigCommerce to share a session or identity token between the main Catalyst storefront and the hosted checkout subdomain? For example:
— Can BC pass a shared session ID or customer token in the checkout redirect URL that we can use to bridge identity?
— Does BC's Catalyst framework expose any server-side hooks or middleware where we could set a root-domain cookie (.domain.com) before the checkout redirect?
— Is there a recommended approach for Klaviyo identity continuity specifically for Catalyst stores using the checkout subdomain?
Any guidance on how BC handles cross-subdomain session bridging for Catalyst storefronts would be greatly appreciated.
