DATETIME saving as 0000-00-00 00:00:00

DATETIME saving as 0000-00-00 00:00:00

This is my sql code ive ran this same code a good amount of times and
never had any issues with it but today or some reason it is.
mysqli_query($con,"INSERT INTO 'u_visits' ('ip_adress','dates') VALUES
('$ip',now()) ON
DUPLICATE KEY UPDATE visits = visits + 1");
mysqli_close($con);
Everything works fine except my dates row gets added as 0000-00-00 00:00:00
thanks in advance for the help.