PS4 error np-31730-4 is an error that usually occurs when the user gets signed out of the PlayStation Network.
Some of the solutions to this error include checking PlayStation server status.
Please see our in-depth walk-through solutions below.
PS4 error np-31730-4 may be caused by server maintenance. Go here to check if the server is under maintenance. If it is, try again later.
If the server is up, try to sign in to the PSN. If it does not let you sign in, go to System Software Update if there is an available update. Also, try to access Safe Mode to double check System Software Update by selecting the option "Update System Software."
To Access Safe Mode
See instruction below or watch it here on YouTube
If none of the above works, PS4 could be under emergency maintenance. Please try after an hour.