It appears that only the testing server at Protx requires protocol 2.23
If a full Protx account has been granted, then carts can be tested against a test server which WILL process protocol 2.22, for the time being.
So, Ecart will work with Protx, but only after a formal application is made and approved.
The free test server, which is available without any committment or merchant number, will not work until Ecart is configured for protocol 2.23
Hope this helps