I found that the documentation is wrong because even though http://server/apt-cacher fails, as long as I point my client to the server apt-cacher is still responding to requests and caching packages locally at /var/cache/apt-cache/packages/.
http://server:3142 , just change the number to the port of apt-cacher.
That works for me. Also adding a /report to the end will give you the usage thus far.
Hope this helps!