Hi Giorgo,

Thank you for getting in touch with us. My name is George, and I'm happy to assist you today. I appreciate your patience while we've been working toward your ticket.

Problems like this are usually caused by configuration issues with web servers such as Apache or Nginx. I'd recommend contacting your web hosting company to look into this since only they can adjust these settings. 

Web server modules like mod_security and other content-filtering solutions might be in place and block requests based on some criteria, like the request body size. That means that your web server automatically rejects requests without consideration because you send more data than it is willing to accept. It's also possible that the hosting provider simply blocks external connections.

As an alternate solution, you can try to manually update the plugin, which involves the same process as installing the it. To do that, you must first log in to your account and download the latest version of LayerSlider. Please note that no password or registration is required; you can log in with any email address using the "Log in with email" option on the right side. Once you're in, your downloads will appear under the Downloads menu, and you can proceed with installation as outlined in this article: https://layerslider.com/documentation/#installation-wp

After updating the plugin manually, please try to activate it again.

I appreciate your understanding!