How many parameters does the callback function in array_reduce expect?

The callback function in array_reduce expects 4 parameters: the accumulated value, the current item in the iteration, the current key, and the array being reduced. If the callback function does not receive these 4 parameters, it will result in an error. To solve this issue, make sure that the callback function has 4 parameters defined in the correct order.

// Example of array_reduce with a callback function that expects 4 parameters
$array = [1, 2, 3, 4, 5];

$sum = array_reduce($array, function($accumulator, $currentItem, $currentIndex, $array) {
    return $accumulator + $currentItem;
}, 0);

echo $sum; // Output: 15