Have just bought into Now; it’s fine on LG tv in main room; bedroom Samsung not allowing me to accept cookies so unable to go past this and watch Nowtv
What is the model number of the Samsung TV?
Basically, you need to go into the Settings, probably System, and look for the option to update the TV’s operating software, but how exactly you reach this depends on the model year of the TV, as included in the model number.
But have a poke about in there, see if you can find it, and if there is a system update, apply it, and then try signing on to Now again.
If there is no update available, then possibly the TV software has gone a bit sideways; unplug the TV from the mains, hold down the physical on/off button on the TV for 30 seconds, wait a further two minutes, and then plug it back in.
No guarantees, but these are the first things to try.