Fatal error – php 8

Hello,

Once upgrading to PHP 8, we encountered a fatal error because of using this function:

add_filter( 'post_class', 'um_add_restricted_class_css', 10, 1 );

function um_add_restricted_class_css($classes){
global $post;
$restriction = get_post_meta( $post->ID, 'um_content_restriction', true );

// if the post is restricted do this.
if ( $restriction['_um_accessible'] == 2 ){
    $classes[] = 'um-restricted-content';
}

return $classes;
}

Can you please advise?

Thank you,

Dan