Why do I need a paid subscription to connect my WordPress.com site?
You can only use Laposta’s WordPress plugins if you are allowed to install plugins on your WordPress website yourself.
If your site runs on wordpress.com, you need a paid subscription for this. You cannot install plugins on a free wordpress.com site. To do so, you must first upgrade to a paid subscription. Having your own domain name makes no difference: even with a custom domain name, you still need a paid subscription on wordpress.com to be able to install plugins.