Hi Wouter,
Thanks a lot for your kind help. With your suggestions I have found the root cause: I have specified the wrong http protocol and port number. I just record it down here in case some other guys have the same problem.
How can I find the correct host name and port for destination configuration
go to your gateway system, tcode SICF, right click the node below and click test service:
Then in the popped up browser window you could identify the protocol name, the host name and the port number.
After I fix my destination configuration file, the issue is gone. Thanks a lot to Wouter for sharing this tip!
Best regards,
Jerry