Jetpack misfunctioning (site inacessible)

Hi,
As mentioned above, I cannot activate Jetpack as it says that my site is not accessible.

I checked a few things:
– the website is open to search engines;
– the xmlrpc.php file is present;
– I deactivated all plugins except Jetpack.

No results. Could you help me understand and solve this problem?

Thanks

https://wordpress.org/plugins/jetpack/