@Gaetz 

That is not a TP-Link Smart switch.  However what looks to be the issue is you appear to have an extra wire comming from the main neutral wire bundle and then wired into a seperate wire nut with the switch.  Eliminate that extra wire and wire the swtich into the main wire nuetral bundle and it should work.  Another possible issue is on the switch you are using the "line" is linked to a white wire, as white is not normally used to carry line or load it might actually be a neutral wire.  For our switches live and load have to be seperate wires.