HomeRunner includes built-in measurement for the booking engine, powered by HomeRunner’s own Google Tag Manager container. You will not find a GTM setting for it in the WordPress backend.
Why this happens. The container is managed inside the HomeRunner plugin itself. It is shared infrastructure that runs across all HomeRunner sites, so access cannot be granted to individual customers or their agencies. It carries only HomeRunner’s booking-engine measurement. Nothing customer-specific lives in it.
What you can do. For your own tracking, use your own GTM container. It can run alongside HomeRunner’s. If your site has the HomeRunner Toolkit’s Conversion Tracking module, you can enter your container ID in the Toolkit dashboard under Conversion Tracking, and HomeRunner loads your container in place of its default one.