ExternalServiceAddAccountCallout.cls

ExternalService.BankService service = new ExternalService.BankService();

//set request
ExternalService.BankService.addAccount_Request req = new ExternalService.BankService.addAccount_Request();

req.accountName = 'GreenMotorCorporation';
req.accountType = 'Customer';
try{
    //make callout
    ExternalService.BankService.addAccount_Response res = service.addAccount(req);
    system.debug('200 response id => '+ res.Code201.id);
    system.debug('200 repsonse: name => '+res.Code201.name);
    system.debug('200 repsonse: available balance => '+res.Code201.availableBal);
    system.debug('200 repsonse: type => '+res.Code201.z0type);

}catch(ExternalService.BankService.getAccount_ResponseException exc){
    system.debug('404 response: error message => '+ exc.code404.errorMessage);
}