Google Cloud DNS: adding Postmaster Tools registration for my Google Cloud DNS domain

hi all,

I have a question on adding my Google cloud domain to Google Postmaster.

I noticed that when i add it , it is automatically Verified. I wanted to get the challenge string so that i can create a TXT DNS record for my domain that will be used for a mail server (that way the challenge string will show up in the drill txt for my subdomain that i am using for this mail server)

For example this is a public verification challenge string for **non-**Google cloud domains that i get to add as a TXT DNS record for my domain

google-site-verification=HzGmxHq8vwedSFeTaqqK5hnWJXJWD0m7zyJHr8q9r5s

((I am using linode domains for the subdomain (it is similar to Route53 on AWS) and would normally add the TXT DNS record there since I am hosting the email service on a VPS on linode.))

My question is, is this expected, that there will be no verification TXT challenge string if one adds a Google DNS Cloud domain to Postmaster.

The link to Postmaster is below so you can see what I am referring to:

https://postmaster.google.com/managedomains

thanks and warm regards
Dave