I had been successfully making GET calls using jQuery to my Web API service, but when I tried a POST, it failed, the request never reaching the breakpoint in my C# code. After using the IE developer tools, I saw that it was pointing to “/sites/apps/MyPost”, and it should have been pointing to “localhost/MyPost”. On the HTML page, there was this line:
<base href="/sites/apps/" />
I commented-out that line, and the POST command was successful.