Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/MathTrig.php
public static function PRODUCT(...$args)
    {
        // Return value
        $returnValue = null;

        // Loop through arguments
        foreach (Functions::flattenArray($args) as $arg) {
            // Is it a numeric value?
            if ((is_numeric($arg)) && (!is_string($arg))) {
                if ($returnValue === null) {
                    $returnValue = $arg;
                } else {
                    $returnValue *= $arg;
                }
            }
        }

        // Return
        if ($returnValue === null) {
            return 0;
        }

        return $returnValue;
    }
public static function PRODUCT(...$args)
    {
        // Return value
        $returnValue = null;

        // Loop through arguments
        foreach (Functions::flattenArray($args) as $arg) {
            // Is it a numeric value?
            if ((is_numeric($arg)) && (!is_string($arg))) {
                if ($returnValue === null) {
                    $returnValue = $arg;
                } else {
                    $returnValue *= $arg;
                }
            }
        }

        // Return
        if ($returnValue === null) {
            return 0;
        }

        return $returnValue;
    }
PRODUCT.

PRODUCT returns the product of all the values and cells referenced in the argument list.

Excel Function:
PRODUCT(value1[,value2[, ...]])

@category Mathematical and Trigonometric Functions

@param mixed ...$args Data values

@return float