Allow Non-administrators to Access the Customizer (Not Working)

The following code added to function file is the stated way to provide access to the customizer for users with “edit_posts” capabilities.

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function allow_users_who_can_edit_posts_to_customize( $caps, $cap, $user_id ) {
    $required_cap = 'edit_posts';
    if ( 'customize' === $cap && user_can( $user_id, $required_cap ) ) {
        $caps = array( $required_cap );
    }
    return $caps;
}
add_filter( 'map_meta_cap', 'allow_users_who_can_edit_posts_to_customize', 10, 3 );

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The Probblem; Outside of the admin, eligible users are shown the customizer link in the toolbar, but when they click the link they get “Cheating,’uh” accusation rather than the customizer.