What playback device are you using, where i am guessing it's a NOW box or NOW Stick ?
Any error code or what is the full message on screen when it says there is a problem ?
if using a NOW Stick / NOW box i am assuming you have tried theses trouble shooting steps in this help guide below.
Sorry can't help any further, has i don't subscribe to the NOW Hayu Membership.
I don't own a PS4 or Smart TV with the Native NOW App on it, but the first things i would try is unplugging the power to your PS4 / Smart TV and Router and maybe try a new download of the NOW App on your devices.
I am also assuming you are not using a VPN or third party Ad blocking software on your Router which sometimes effects the running of the NOW App.
Hopefully another forum member will come up with more suggestions to try to get your NOW Hayu Membership up & running again.
If you have an LG Smart TV and none of the suggestions help so far, then i would be tempted to try this in this linked thread below even though the error message is different.
Another thing i would try is type "PS4 Something not Right" or "LG Something not Right" which seems to be a common occurrence in the Community search box to see if anybody on the hit results have a solution that works for your particular case.