Hi Everyone,
I'm new to rest webservices.
for the integration superbadge I developed below code under Synchronize Inbound Project Data.
@RestResource(urlMapping='/project/*')
global class ProjectRESTService {
    //Implement service logic here
    
    @HttpPost
    global static string postProjectData(String ProjectRef, String ProjectName,string OpportunityId,
        Date StartDate, Date EndDate,Double Amount ,String Status) {
        string response ;
        Project__c proj =[select Billable_Amount__c,End_Date__c,Opportunity__c , ProjectRef__c,
                            Start_Date__c , Status__c from Project__c where ProjectRef__c =:ProjectRef];
        if(proj == null )
        proj = new Project__c();
        proj.ProjectRef__c = ProjectRef ;
        proj.Name = ProjectName ;
        proj.Opportunity__c  = OpportunityId ;
        proj.Start_Date__c = StartDate;
        proj.end_Date__c = EndDate;
        proj.Billable_Amount__c = Amount ;
        proj.Status__c = status ;
        opportunity optytoUpdate = new  opportunity(Id =OpportunityId  );
        optytoUpdate.DeliveryInstallationStatus__c = 'In progress' ;
        try{
            update optytoUpdate ;
             upsert proj  ;
             response  ='Ok';
          }
          catch(Exception ex){
              response   = 'Error Occured : '+ ex.getMessage();
          
          }   
        return response   ;
    }   

}

Now wondering how to test it.
As described when opportunity is updated to closed won Stage is succesfully updated to Submitted Project. 
inbound call does not happen after that. how do i troubleshoot?