Hi..

Try below code...u missed ( } --last line)

global class MainClass
{
global class RequestClass
{
webservice String errorMessage;

//Account Releated Fields

global Class AccountWrapper // Line9
{
webservice String accName;
webservice Integer accNumber;
webservice Id AccountId;
webservice List<AccountWrapper> accounts;
webservice List<ContactWrapper>;
webservice List<OpportunityWrapper>;
}

//Contact Releated Fields
//webservice String contactName;
global class ContactWrapper
{
webservice String clName;
webservice String cfName;

}

// Opportunity Releated Fields
global class OpportunityWrapper
{
webservice String oName;
webservice String ocDate;
webservice String oStage;
webservice List<ProductWrapper>;
}
// Quote Realeted Fields
webservice String qName;




// Product fields
global class ProductWrapper
{
webservice String productcode;
webservice String productName;
// boolean active;
webservice Integer quantity;
webservice Integer unitprice;
}
// QuoteItem Fields

webservice String qitemName;


}

webservice static ResponseClass behaviourOfWebService(RequestClass req)
{

List<Account> accountList = new List<Account>();
Account a;
for(AccountWrapper wrapper: req.accounts){
a = new Account();
a.Name = wrapper.accName;
a.AccountNumber =String.valueOf(wrapper.accNumber);
accountList.add(a);
}
insert AccountList;

ResponseClass res = new ResponseClass();
res.resId = a.Id;
res.resName = a.Name;
res.cresName = c.FirstName;
// res.respId = p.Id;
return res;
return res;

}
}

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Thanks,

Cool Sfdc