I see it is hard-coded to not allow mapping if
blog_id is 0 or 1? Is it to block mapping for main blog/site of the network? Then shall the plugin check for
BLOG_ID_CURRENT_SITE value in
wp-config.php instead of hard-coded values?
For example in our case, the blog with id = 1 is not the main one but the blog id 3 is the main site:
define('BLOG_ID_CURRENT_SITE', 3); and this plugin doesn't allow mapping for the blog id 1.