Getting this error after entering the monitored instance connection details...
ora 12545 connection failed because the target host or object does not exist
This is caused by a DNS issue between the middleware host and monitored instance – this is verified if ping is successful only when using the FQDN (ie cannot ping using only the machine name)
To resolve this issue, either update the /etc/hosts file on the middleware server and verify ping is successful using both the monitored machine name and FQDN. If this is not possible try selecting the cluster option and enter the FQDN as the virtual name which will force the installer to use the FQDN of the monitored server as an alias and allow the install to complete successfully.