"Unsupported version of FortiClient" message

[pablob127]

A few days ago my VPN stopped working, in the following way:

I can login correctly and the tunnels seem to be correctly set up. However, when I try to connect to any computer on the other side I simply cannot connect. From a traceroute, the packets do not even seem to reach the other end of the tunnel.

When I try to access the website, I get the following message:

  It seems you are using an unsupported version of FortiClient.                 
                                                                                
   Please disconnect your current VPN connection and download the official      
   supported version of FortiClient from the <website>               

I have tried with both the openfortivpn included in Debian 12 (1.19.0), and 1.22.1 (compiled by myself), and the behaviour is the same. I think that something changed in the VPN configuration that tries to enforce the Fortinet client. Do you think there may be any workarounds to avoid having to use that client?

Thanks!