Single sign out (api/ client adapter)

Hi. We built Single Sign On system using 3 apps as client and keycloak as oidc provider.
All apps installed by using helm chart on kubernetes.
Single sign-on works well. But we’re struggle with single sign out.
From a log-out of one app, the session is closed on keycloak.
But other apps continuously stay in log-on state.
I guess We need to use the “BackChannel Log out URL” to single sign-out.

To enable to use backchannel log out by client side,
should I make an api on client apps to receive the logout token
or something related with backchannel log out?
Or should I use client adapter?