Get Every Key & Value from Array then Display All in New Line

if you can print your array why cant’ you just do a loop on this array and adding each line into your output_content.
It will look like this

<?php
$myArray = Array
(
    0 => Array
        (
            0 => "Color",
            1 => "Black",
        ),

    1 => Array
        (
            0 => "Size",
            1 => "M",
        ),

    2 => Array
        (
            0 => "Gift",
            1 => "Tes 2"
        ),

);
$output_content = "";
foreach($myArray as $key){
    $output_content .= $key[0]." : ".$key[1]."\r";
}
echo $output_content;

?>

And this code prints :

Color : Black
Size : M
Gift : Tes 2