Data Integration Specialist Superbadge - Step 7

[meghanchrls6]

I'm getting an error message when triggering the SOAP call from the UI via record update:

System.CalloutException: IO Exception: External server did not return any content

When I import the WSDL into SOAP UI and send the same package body, I receive this message:
HTTP /1.1 500 
Server: Cowboy
Content-Type: application/json;charset=UTF-8
Transfer-Encoding: chunked
Date: Mon, 10 Jul 2017 17:58:08 GMT
Via: 1.1 vegur
Proxy-Connection: Keep-Alive
Connection: Keep-Alive

Does this mean that the herokuapp needs to be restarted or something? Even when i was getting trained on Salesforce also this topic was not discussed in detailed. I've found a couple of posts with sample code for this challenge and with a few small differences, mine matches from what I can tell. Here's the code I'm using:

ProjectTrigger

trigger ProjectTrigger on Project__c (after update) {
    //Call the Billing Service callout logic here

    if (trigger.isAfter && trigger.isUpdate) {
        BillingCalloutService.callBillingService(Trigger.new, Trigger.newMap, Trigger.old, Trigger.oldMap);
    }

}

BillingCalloutService

public class BillingCalloutService {
    //Implement business and callout logic methods here
    public static void callBillingService(List<Project__c> newList, Map<Id, Project__c> newMap,
            List<Project__c> oldList, Map<Id, Project__c> oldMap) {

        if(!newList.isEmpty()) {
            Project__c project = newList[0];
            if (project.Status__c == 'Billable' && oldMap.get(project.Id).Status__c != 'Billable') {
                // Get Service Credentials from custom settings
                ServiceCredentials__c credentials = ServiceCredentials__c.getInstance('BillingServiceCredential');
                billProject(project.ProjectRef__c, project.Billable_Amount__c, credentials.Username__c, credentials.Password__c);
            }
        }
    }

    @Future(callout=true)
    private static void billProject(String projectRef, Decimal billAmount, String username, String password) {

        BillingServiceProxy.project project = new BillingServiceProxy.project();
        project.projectRef = projectRef;
        project.billAmount = billAmount;
        project.username = username;
        project.password = password;

        BillingServiceProxy.InvoicesPortSoap11 invoiceCall = new BillingServiceProxy.InvoicesPortSoap11();
        // Make the callout and update the Status if callout is successful
        String response = invoiceCall.billProject(project);

        List<Project__c> projects = new List<Project__c>();
        if(response != null && response.equalsIgnoreCase('OK')) {

            projects = [
                    Select Id, Status__c
                    From Project__c
                    Where ProjectRef__c = :projectRef
            ];
            if(!projects.isEmpty()) {
                projects[0].Status__c = 'Billed';
                update projects;
            }
        }

    }
}

BillingServiceProxy

//Generated by wsdl2apex

public class BillingServiceProxy {
    public class billProjectRequest_element {
        public BillingServiceProxy.project project;
        private String[] project_type_info = new String[]{'project','http://salesforce.com/th/invoice-web-service',null,'1','1','false'};
        private String[] apex_schema_type_info = new String[]{'http://salesforce.com/th/invoice-web-service','true','false'};
        private String[] field_order_type_info = new String[]{'project'};
    }
    public class project {
        public String username;
        public String password;
        public String projectRef;
        public Double billAmount;
        private String[] username_type_info = new String[]{'username','http://salesforce.com/th/invoice-web-service',null,'1','1','false'};
        private String[] password_type_info = new String[]{'password','http://salesforce.com/th/invoice-web-service',null,'1','1','false'};
        private String[] projectRef_type_info = new String[]{'projectRef','http://salesforce.com/th/invoice-web-service',null,'1','1','false'};
        private String[] billAmount_type_info = new String[]{'billAmount','http://salesforce.com/th/invoice-web-service',null,'1','1','false'};
        private String[] apex_schema_type_info = new String[]{'http://salesforce.com/th/invoice-web-service','true','false'};
        private String[] field_order_type_info = new String[]{'username','password','projectRef','billAmount'};
    }
    public class billProjectResponse_element {
        public String status;
        private String[] status_type_info = new String[]{'status','http://salesforce.com/th/invoice-web-service',null,'1','1','false'};
        private String[] apex_schema_type_info = new String[]{'http://salesforce.com/th/invoice-web-service','true','false'};
        private String[] field_order_type_info = new String[]{'status'};
    }
    public class InvoicesPortSoap11 {
        public String endpoint_x = 'http://sb-integration-bs.herokuapp.com:80/ws';
        public Map<String,String> inputHttpHeaders_x;
        public Map<String,String> outputHttpHeaders_x;
        public String clientCertName_x;
        public String clientCert_x;
        public String clientCertPasswd_x;
        public Integer timeout_x;
        private String[] ns_map_type_info = new String[]{'http://salesforce.com/th/invoice-web-service', 'BillingServiceProxy'};
        public String billProject(BillingServiceProxy.project project) {
            BillingServiceProxy.billProjectRequest_element request_x = new BillingServiceProxy.billProjectRequest_element();
            request_x.project = project;
            BillingServiceProxy.billProjectResponse_element response_x;
            Map<String, BillingServiceProxy.billProjectResponse_element> response_map_x = new Map<String, BillingServiceProxy.billProjectResponse_element>();
            response_map_x.put('response_x', response_x);
            WebServiceCallout.invoke(
              this,
              request_x,
              response_map_x,
              new String[]{endpoint_x,
              '',
              'http://salesforce.com/th/invoice-web-service',
              'billProjectRequest',
              'http://salesforce.com/th/invoice-web-service',
              'billProjectResponse',
              'BillingServiceProxy.billProjectResponse_element'}
            );
            response_x = response_map_x.get('response_x');
            return response_x.status;
        }
    }
}

Can you help me where i have done mistake?

Thanks!