key URL
after you generate a sender/receiver key pair for your channel, you should post the receiver key (from the receiver_keys folder) to your web server.
the key URL must point to where your receiver key is on the web. For example, if your channel is called "testChannel", you need to upload testChannel.key from your receiver_keys folder to your web server. If you upload it to a "keys" folder on www.myweb.com, your key URL would be:
http://www.myweb.com/keys/testChannel.key