Featured Image from Blog Posts not showing when sharing link on Social Media

Hello,
When I share a blog post for example on Facebook the Featured Image I have included in the blog post does not show. Instead, my Logo shows. I investigated this and was told by Facebook’s Debug Tool that –

Warnings That Should Be Fixed: Inferred Property
The ‘og:image’ property should be explicitly provided, even if a value can be inferred from other tags.

I then investigated further and was told by AI to add the following code to the theme’s functions.php file:

function add_open_graph_tags() {
if (is_single()) {
global $post;
$thumbnail = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID), ‘large’);
if ($thumbnail) {
echo ‘<meta property=”og:image” content=”‘ . esc_url($thumbnail[0]) . ‘” />’ . “\n”;
}
} elseif (is_home() || is_front_page()) {
// You can set a default og:image for your homepage here
echo ‘<meta property=”og:image” content=”URL_OF_YOUR_DEFAULT_IMAGE” />’ . “\n”;
}
}

The thing is that I don’t know what the URL_OF_YOUR_DEFAULT_IMAGE is. I tried with a random image url from my WordPress Media folder but the FB Debugger did not like that, either.

Can you please help? Many thanks and greetings, Lokita