Please, how do I add seller's contact and business profile link to the sidebar just like the one in the picture I have attached.

@felixbmens
There used to be osc_user_public_profile_url() function.

Please do you have it?

@felixbmens
There used to be osc_user_public_profile_url() function.

It's already in core.
function osc_user_public_profile_url($id = null) {
        if($id==null) {
            $id = osc_user_id();
        }
        if ($id != '') {
            if ( osc_rewrite_enabled() ) {
                $user = User::newInstance()->findByPrimaryKey($id);
                $path = osc_base_url().osc_get_preference('rewrite_user_profile')."/".$user['s_username'];
            } else {
                $path = sprintf(osc_base_url(true) . '?page=user&action=pub_profile&id=%d', $id);
            }
        } else {
            $path = '';
        }
        return $path;
    }