Let's encrypt certificate and Remote Access SSL VPN configuration

Hello and happy new year to everybody!

I try to configure the SSL Remote Access VPN with Let's Encrypt certificate.

Here is my configuration

When I try a connection, it fails after some tries with this log (I'm on Linux, so I've just import the ovpn file for my user)

Jan 13 12:00:38 PORT-MAISON05 nm-openvpn[7681]: SIGUSR1[soft,connection-reset] received, process restarting
Jan 13 12:05:38 PORT-MAISON05 nm-openvpn[7681]: NOTE: the current --script-security setting may allow this configuration to call user-defined scripts
Jan 13 12:05:38 PORT-MAISON05 nm-openvpn[7681]: TCP/UDP: Preserving recently used remote address: [AF_INET]XXX.XXX.XXX.XXX:443
Jan 13 12:05:38 PORT-MAISON05 nm-openvpn[7681]: Attempting to establish TCP connection with [AF_INET]XXX.XXX.XXX.XXX:443 [nonblock]
Jan 13 12:05:39 PORT-MAISON05 nm-openvpn[7681]: TCP connection established with [AF_INET]XXX.XXX.XXX.XXX:443
Jan 13 12:05:39 PORT-MAISON05 nm-openvpn[7681]: TCP_CLIENT link local: (not bound)
Jan 13 12:05:39 PORT-MAISON05 nm-openvpn[7681]: TCP_CLIENT link remote: [AF_INET]XXX.XXX.XXX.XXX:443
Jan 13 12:05:39 PORT-MAISON05 nm-openvpn[7681]: Connection reset, restarting [0]

I think I miss something and I'm pretty sure that the UTM continue to use the default certificate instead of the Let's Encrypt certificate for the VPN connection.

Did you know how to change this and if there is any error in my configuration ?

I've also add a masquerading rule from Any to the WAN interface.

Thank you for your help!

John