Hubspot, Google Tag Manager and cookie consent

Please disregard this post. Subdomains are hosted in Hubspot but main domain is external - so I wont be able to implement GTM via Hubspot in terms of the main domain… but I still need to get GTM and the Hubspot consent solution to work on the main domain (works on the hosted subdomains where GTM is also integrated with Hubspot).
Hope for your assistance