I invoked the API by postman successfully but did not in HttpClient as the shown below. And there are no logs in wso2carbon.log or error.log
javax.net.ssl.SSLException: hostname in certificate didn't match: <14.201.60.216> != <localhost>
and Do I have to generate my own KeyStore if I want to use httpclient to inovke the linux's API?
You will have to create a new keystore with CN as your domain. Follow this tutorial https://medium.com/@dunithd/wso2-das-how-to-fix-javax-net-ssl-sslexception-160c13bc8fe7#.tgh16eu4s