mysqli_query($con, $update) or die(mysqli_error()); mysqli_error() expects exactly 1 parameter, 0 given in code example

Example: Warning: mysqli_error() expects exactly 1 parameter, 0

Change

die (mysqli_error()); 
to

die('Error: ' . mysqli_error($myConnection));
in the query

$query = mysqli_query($myConnection, $sqlCommand) or die (mysqli_error());