In order to check whether the domain is delegated, you can go to xnnd.com  and input the domain in question. If the domain is not showing as delegated, refer to the G Suite Toolbox to see if the NS entries are showing publicly or if an SOA field is in place.

If the NS entries are not showing, please reach out to your IT team and ensure the records are set to be public.
 

If you see "SOA" in the results, this would indicate that there is an SOA record that is preventing the delegation from working properly. We would recommend engaging with your IT team to have them remove the SOA record before attempting to fill out the form.