Could you remove the connection between the TV and the phone/ Forget the connection?
Then, could you go into your Gallery on your phone and select a photo? After this, tap share and then press on the Smart View button. Does this connect?
I have upgraded my phone to the S8. Made sure all the updates are done then tried the smart view. Sadly I'm still getting the same error message.
Could this his be a problem with my Tv?
With the same error appearing with your S8 it would lead me to believe that the issue is either with the TV or the type of router you are using as some routers do not allow pass through connections to other devices, only access out to the internet (these are usually mobile network routers.)
Other than that, this is how the device should connect to the TV:
Another thing to check is that they're both connected under the sme band to the router, as some routers have connections under 2.4GhZ and 5GhZ - if they are both connected to separate frequency's this could also cause it not to connect (That is if the TV is connected wirelessly - if via Ethernet cable there should be no problem here).
I can't find the screen mirroring input on my Tv. Not sure where to find the frequency settings on either device. I'm using a sky broadband router. The screen mirroring worked once this morning but has now stopped again.