Source Button

I can not get our Sofabaton U1 remote to replace the functions of my Samsung TV (model number UN32M4500AE) remote. I've managed to use a "work around" for every button using the Xfinity remote and the Harmony 650 remote we're replacing. The only button that I haven't been able to get to work is the Source button - the one that should bring up our menu of streaming services. On our TV remote it's right next to the power key but whenever I try to use the "Learn From Original Remote Key" the screen says it has learned successfully. However, when I push the button, nothing happens. I tried to "Reassign Remote Key" to the TV Input key from the Xfinity remote and this didn't work although it did say "loading". Any help will be very much appreciated as this is the last hurdle to successfully replace the original remotes and old Harmony.