Jetpack doesn't connect to WordPress

Hi there,
we can’t connect our website to the magnificient jetpack service.

When we try we have back this message:

Invalid request, please go back and try again.
Error Code: invalid_client
Error Message: Unknown client_id.

If we use the debugger we have got that message:

[body] => {‘error’:’Could not validate security token’,’error_description’:’We were unable to validate a security token for Jetpack communication. Please try disconnecting Jetpack from your WordPress.com account, and connecting it again.’}

Please help us

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