Please ensure you have SAM Cast set up to use the HTTP Event adaptor on port 8181.
Go to SAM Cast->Settings->Event Adaptors and then select the HTTP event adaptor and set it to operate on port 8181.
If your firewall requests to allow access, please allow this or place an exception rule in your firewall that enables SAM Cast to operate on this port.
You need to load this page on the SAME machine that is running SAM Cast.
Also make sure you Stop and then Start SAM Cast to ensure the HTTP adaptor is loaded.