Connecting Smartphone and Smart TV Roku Apps

There are three requirements for the Roku app to connect to a Roku device. First, they must both be on the same network. That doesn't mean they both have to be connected to the same access point, or even using the same radio band (2.4 or 5GHz). Second, the network must be using an IP address range that is within the IANA specified as Private. Most home routers use a private IP address range by default, but I have encountered routers that someone changed the IP address range to something considered Public. The Roku app will not work on a public IP address network. The final thing that has to be correct is the WiFi network must NOT be using a security setting that blocks connected devices from seeing other devices on the network. This is common in hotels, dorm networks, or public networks found in stores and coffee shops. If it's enabled on your home network, then no WiFi connected device can see anything on your local network, regardless if it's wireless or wired. 

My guess is the third option is the cause of your lack of connection. If this is your home network, then check your WiFi access point (usually your home router) and look for that security setting. If you're using any sort of shared WiFi (apartment complex, work, hotel, dorm) then you're never going to be able to use the app to control your Roku TV. 

However, now that I've gone through all of that, I see your real problem. The Roku app will not and cannot control the Roku Channel app on a non-Roku TV. You can only use your Samsung TV remote to control the apps installed on your TV. There is no way the Roku app can control an app on a non-Roku TV. And the same would apply to any other app installed on your Samsung TV. The Samsung remote is the only way to control anything on that TV.