Unable to Sync all the instances from the AWS to the Ansible Tower

[Vishakh]

I have around 30 Server Instances in AWS all having only the Private IP. 

In the ansible tower, I have used AWS access key and secret key and thus configured the credentials in the tower.

When I start creating a new inventory, i fill all the necessary params in the inventory sources and then I sync the inventory. After syncing, I am able to see 2 or 3 instance in the host tab.

I cannot see other hosts.

Please help me resolving this issue.