wpsl_thumb_size is not working

I have been trying to update the size of the thumbnail in my archive page but it not updating.

add_filter('wpsl_listing_template', 'custom_listing_template');

function custom_listing_template()

{

? ? global $wpsl, $wpsl_settings;

? ? $listing_template .= "\t\t\t" . '<figure><%= thumb %></figure>' . "\r\n";
//....other
? ? return $listing_template;

}

// Image size to update the image
add_filter('wpsl_thumb_size', 'wpsl_kodiak_thumb_size');



function wpsl_kodiak_thumb_size()

{

    //$size = array(250, 250);
    $size = 'medium';

    return $size;

}

Please help!!

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