Server connect ERROR

Hi, I have wappler 3.5.1 but the connect server no longer works, the problem is when I create a connection to the db …
I paste the error thanks

{“code”: 0, “file”: “\ / home \ / … \ / app … er … \ / dmxConnectLib \ / lib \ /db/Connection.php”,“line”:36,“message”:"Connection String is Required “,” trace “:” # 0 \ / home \ / phonerec \ /app.phone-recovery.it \ / dmxConnectLib \ / modules \ /dbconnector.php (12): lib \ db \ Connection -> __ construct (Object (lib \ App), Object (stdClass), ‘connection_1’) \ n # 1 \ / home \ / phonerec \ / app … it \ / dmxConnectLib \ / lib \ /App.php (199): modules \ dbconnector-> connect (Object (stdClass), ‘connection_1’) \ n # 2 \ / home \ / phonerec \ /a…p … it \ / dmxConnectLib \ / lib \ /App.php (163): lib \ App-> execSteps (Object (stdClass )) \ n # 3 \ / home \ / phonerec \ / app … it \ / dmxConnectLib \ / lib \ /App.php (133): lib \ App-> execSteps (Array ) \ n # 4 \ / home \ / phonerec \ / app … it \ / dmxConnectLib \ / lib \ /App.php (116): lib \ App-> exec (Object (stdClass), false) \ n # 5 \ / home \ / phonerec \ / app … it \ / dmxConnectLib \ / lib \ /App.php (94): lib \ App-> exec (Object (stdClass)) \ n # 6 \ / home \ / p … c \ / app … it \ / dmxConnect \ /api/vers_2/settings/prova.php(8): lib \ App-> define (Object (stdClass)) \ n # 7 {main} "}