Checkbox Wordpress not checking

I had to edit the code of someone else, it's a plugin in Wordpress but i'm kinda stuck here.

    <?php
            woocommerce_wp_checkbox( 
            array( 
                'id'            => 'per3',              
                'label'         => __('Per 3', 'woocommerce' ), 
                'description'   => __( 'ja', 'woocommerce' ),
                'value'     => $variation_data['per3'][0]
            )
        );  
        ?>

This is the array part , and at Per 3 it's supposed to be checked and stay checked however,

function variable_fields_process( $post_id ) {
if (isset( $_POST['variable_sku'] ) ) {
    $variable_sku = $_POST['variable_sku'];
    $variable_post_id = $_POST['variable_post_id'];
    $variable_custom_field = $_POST['per3'];
    for ( $i = 0; $i < sizeof( $variable_sku ); $i++ ) {
        $variation_id = (int) $variable_post_id[$i];
        if ( isset( $variable_custom_field[$i] ) ) {
            update_post_meta( $variation_id, 'per3', stripslashes( $variable_custom_field[$i] ) );
        }else{
            delete_post_meta( $variation_id, 'per3', stripslashes( $variable_custom_field[$i] ) );
        }
    }
}

This is the process part, and i'm not a advanced coder at all, so this doesn't tell me a whole lot other than that there's no way in it to save , i've tried different stuff like checking the box, but to no avail.