Hi,
Thank you for posting in our forum.
To correctly resolve the managed domain from the on-premises environment, you may need to add forwarders to the existing DNS servers. If you haven't configured the on-premises environment to communicate with the managed domain, complete the following steps from a management workstation for the on-premises AD DS domain:
Select Start > Administrative Tools > DNS.
Right-select DNS server, such as myAD01, then select Properties.
Choose Forwarders, then Edit to add additional forwarders.
Add the IP addresses of the managed domain, such as 10.0.2.4 and 10.0.2.5.
reference:https://learn.microsoft.com/en-us/azure/active-directory-domain-services/tutorial-create-forest-trust
Hope this information can help you
Best wishes
Vicky