Add Secondary to Replica Set in MongoDB Windows
As per the error message says, you have added the Primary node of the replica set as localhost. The rule is all nodes of the replica set should be localhost or all should be hostname/ip address.

If you run rs.status() from primary, you will see the primary replica set member as localhost. So when you try to add a secondary with rs.add("192.168.56.136:27017") the system will throw an error.

How to correct this?

conf = rs.conf()

update the hostname of primary member in conf variable

then run

rs.reConfig(conf)

Now add the secondary member.