The external consultant proposed another way, which is to use OLE Automation, while we managed to make it work occasionally, it seems to be unreliable at all. The cause of this is still unclear, I will look back once I get more timee.
After all, we know that the native way to call external web service is to use CLR and create assembly, since I haven’t done this before, it will be quite interesting to figure out how it works. So far, I have managed to create the CLR assembly and made it working. No sure why the other two methods didn’t work, but this final approach works pretty well.