Add Custom Domain: DNS record for the subdomain

Hi, I am creating a GTM SS container in order to use it for FB API with Unbounce landing pages.
According to our system administrator IF i follow point 8. b) use a custom subdomain, the new A record will redirect our subdomain to Stape’s server or container ( where the IPv4 address points to ).
According to him this would create a Problem since currently the subdomain points to Unbounce using it current A record in the DNS.

Can you help clarify why we encounter this issue and what can we do in order to proceed with the GTM SS container?

This is the article if follow:

Thank you in advance

Your admin is right. You need to use a new subdomain for the GTM Server Side container.
For example, if you have then you should set up a subdomain as or depends on your needs.

This topic relates to this one How do I link the GTM-server IP to subdomain on shopify?

Thank you very much for the response.
So in summary what you advice is to create a new subdomain for the GTM SS container ( ), if there is a CNAME automatically created we should delete it and leave the A record pointing only to We are using Cloudflare.

I saw the case you send me, the user states that in the end the new subdomain page returned only 404 error…