Inserting PHP not working

Hello, I'm trying to use the Visual Portfolio plugin to customise a post gallery. To do so, the plugin propose to insert a PHP function in the documentation :

add_filter( 'vpf_extend_tiles', 'my_filter_vpf_extend_tiles' );

function my_filter_vpf_extend_tiles( $tiles ) {
    return array_merge( $tiles, array(
        array(
            
            'value' => '6|1,1|1,1|1,1|1,1|2,1|2,1|',
        ),
        
    ) );
}

I add it to my function.php file and try to use it playing with different values, but it doesn't work, nothing happen frontend.

Would you have any clue why the function is not working ?