@sunnagar: The problem is that the orchestrator cannot connect with the host you are trying to add using the hostname. The fact that the addition is possible when you specify the address point toward a change in the lab DNS has happened and now you cannot use the hostname to connect with the new hosts using ssh. Please verify the DNS problem in the automation lab, or test the operation in an environement where the identification of the hosts using the hostname will be possible.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Red Hat Ceph Storage 5.0 bug fix and enhancement), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2021:3294