The plugin gets stuck like shown in above screenshot.
It also shows the following error at the log.
java.lang.IllegalArgumentException: Illegal character in path at index 59: http://myserver.com/tk/rest/plugins/1.0/${atlassian.plugin.key}-key
at java.net.URI.create(URI.java:852)
at javax.ws.rs.core.UriBuilder.fromUri(UriBuilder.java:95)
at com.atlassian.plugins.rest.module.RestDelegatingServletFilter$JerseyOsgiServletContainer.doFilter(RestDelegatingServletFilter.java:171)
at com.sun.jersey.spi.container.servlet.ServletContainer.doFilter(ServletContainer.java:795)
at com.atlassian.plugins.rest.module.RestDelegatingServletFilter.doFilter(RestDelegatingServletFilter.java:73)
... 101 filtered
at com.atlassian.plugins.rest.module.servlet.RestSeraphFilter.doFilter(RestSeraphFilter.java:40)
... 73 filtered
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745