Getting error Message plugin Free Books Section

After Installing the plugin Free Book section saved the required settings and opened a new page and inserted the short code.

While checking the page getting the following error:

Forbidden

You don’t have permission to access /plugin/fbs.htm on this server.
Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.

Even could not open the home page of the concerned plugin

http://www.whitedovebooks.co.uk/plugin/fbs.htm

Can you Pl check and revert….

https://ww.wp.xz.cn/plugins/free-books-section/