Save Error: Missing Return Statement Required return type string

I am a beginner, I wrote this code to basically take two JSON POSTS and combine them I am getting a Save Error: Missing Return Statement Required return type string. My code is as follows, any help would be great! I have a return statement and it is a string so i'm not sure what I am missing.  global with sharing class SendMCAwFiles { global SendMCAwFiles (ApexPages.StandardController stdController) @RemoteAction global static String submittoMCAwDocs(List<Id>attachmentIds, String parentId, String mcaSubmissionID, String app_id,boolean allow_resubmit) { List<String> files = new List<String>(); String documentUL_json; String response; MCA_Submission__c mcaSub = [SELECT Id,App_ID__c, Error_Message__c,FP_URL__c, Submission_Date_Time__c,FP_Username__c, FP_Password__c, Opportunity__c FROM MCA_Submission__c WHERE Id = :mcaSubmissionId]; for (String attachmentId : attachmentIds) { documentUL_json = ''; response = ''; cg__OpportunityFile__c file = [SELECT Id, cg__File_Size__c, CreatedDate, MCA_Doc_Type__c, cg__Content_Type__c, cg__File_Name__c, MCA_File_Upload_Date__c FROM cg__OpportunityFile__c WHERE Id = :attachmentId]; string fileURL = cg.SDriveTools.getAttachmentURL(parentId, attachmentId, 7200000); system.debug('UPLOAD FILE: ' + file.Id + ', URL: ' + fileURL); documentUL_json = MCAJSONUploadDocument.MCAJSONUploadDocument( mcaSub.FP_Username__c, mcaSub.FP_Password__c, mcaSub.Id, file.MCA_Doc_Type__c, file.cg__File_Name__c, fileURL // now all documents that are attached are stored withing the DocumentUL__Json string if(mcaSub.App_ID__c != null && !allow_resubmit) { system.debug('App has already been submitted.'); } else { String jsonRequest=MCAJsonConstruct.MCAJsonConstruct(mcaSubmissionID); System.debug('MCA Json Request: ' + jsonRequest); Datetime currentDateTime = Datetime.now(); String results; String DocwSub = documentUL_json + jsonRequest; try { Http httpProtocol = new Http(); HttpRequest request = new HttpRequest(); request.setEndPoint(mcaSub.FP_URL__c+'submit_application with documents'); request.setMethod('POST'); request.setTimeout(120000); request.setHeader('Content-Type', 'application/json'); // set body to DowwSub which is the String for hte document attachment plus the Object. request.setBody(DocwSub); HttpResponse json_response = httpProtocol.send(request); String response2 = json_response.getBody(); System.debug('MCA Json Response: ' + response); JSONParser parser = JSON.createParser(response); string IsError=''; string Message=''; string RowId=''; //parser response while (parser.nextToken() != JSONToken.END_OBJECT) { if (parser.getCurrentToken() == JSONToken.FIELD_NAME) { String text = parser.getText(); String fieldName = parser.getCurrentName(); if (parser.nextToken() != JSONToken.VALUE_NULL) { if (text == 'IsError') { IsError = parser.getText(); } else if (text =='Message') { parser.nextValue(); Message = parser.getText(); } else if (text == 'RowId') { RowId= parser.getText(); } else { System.debug(response); } // end while if(IsError == 'false') { mcaSub.App_ID__c = RowId; results = 'Send to MCA was: ' + Message; } else { results = 'There was a problem: ' + Message; System.debug('PROBLEM: ' + Message); mcaSub.Submission_Date_Time__c = currentDateTime; mcaSub.Error_Message__c = Message; update mcaSub; } catch(System.CalloutException e) { System.debug('FAILED: ' + e); results = 'ERROR: ' + e; return results; } // end if (mca.App_ID__c != null && !allow_resubmit) } // end Pequalwdocs }