I just found this iOS error code guide under the NowTV help centre where there is a small section about error code 16.
Out of curiosity are you seeing error code 16 on everything you try to watch with your NowTV pass or only one particular TV show or episode ?
So the error 16 code is only coming up on one particular TV show.
What's the name of the TV show ?
Sounds to me if it's only one TV series in question and other TV shows work on the NowTV App then there is a glitch between your iPhone and the NowTV app TV show.
Maybe post the name of the TV series so somebody who owns an iPhone on here can check if the TV episode plays on their phone to see if they are seeing the same issue.
Unfortunately i don't own an iPhone to check myself.
I am guessing you have tried switching the power off to both your iPhone and let it reboot up again and at the same time reboot your Router as well.
Perhaps see if live chat can assist you further.
Have you rebooted your iPad?
The easiest way is to use the option Settings/General/Shutdown, if you have this, which on more modern iPads, I believe is the only way.
On older iPads like my 2016 Pro, though, you can hold down the On/Off button until the iPad asks you to confirm you want to power off, you slide the onscreen slider, and it powers off.
Either way, you then give it two minutes for the electrons in volatile memory to die, which includes the NowTV cache, and then hold the On/Off button in - for quite a few seconds - until it starts powering up again.