If I try to install this add-on (the XML) I am getting "Request not validated" as an error message.
Could you please send us an admin account via conversation to check your issues ?
Registered an restricted admin account, tried it again (to be sure, that you can do everything what you need to do) and installation worked well now.
A bit strange, maybe some issues with the connection to your servers?!
Yes, we also think this because some issues from connection.
We saw that you installed on your site. Let us know if you have any other issues.