Sample plugin deployment failed in vSphere client 6.7

I have used VMware ESXi 6.7.0 (build-103026080) and installed vCenter Server VMware-VCSA-all-6.7.0-15132721.

I have built the remote-plugin-sample from html-client-sdk and successfully registered the plugin "remote-plugin-sample-6.7.0-SNAPSHOT.jar".

In vSphere client plugins Sample plugin deployment got failed. It showing an error "Error downloading plug-in. Make sure that the URL is reachable and the registered thumbprint is correct. java.net.ConnectException: Connection refused (Connection refused) java.net.PlainSocketImpl.socketConnect(Native Method)".

I have verified the thumbprint value that is correct. I am able to fetch the plugin.json file(https://localhost:8443/sample-ui/plugin.json).

Please suggest me how to proceed further.