GST E-Invoice API Integration Explained

Dear Reader, GSPs/ASPs & Dynamics NAV Service Provider/Consultants are too busy to integrate E-Invoice solutions. Taxpayers with Turnover between Rs 100 Cr- Rs 500 Cr can contact the GSP / ERPs for the willingness to integrate the e-Invoice APIs through them.

Lots of solutions being offered. Customers are in rush to get it done ASAP as dead line is approaching.

Mostly solution are opted by customer:

1. API : Plain Text  
2. API : With Encryption & Decryption
3. SFTP file transfer (Excel/CSV/JSON)

Further solutions are offered with two type of schema:

1. GSP's own schema
2. Government Compatible

Below I am explaining solution step by step, how to integrate E-Invoice APIs.

Hope all of us are aware about Microsoft has already given solution (can be checked in recent Cumulative updates & can be found on Posted Sales Invoice / Credit Memo):

1. Generate IRN
2. Export Json File
3. Import Json File

There is a codeunit ID; 16511 with Name: e-Invoice, for export & import JSON request & response based on Government Schema (based on NIC portal & can be checked here). Which is provided by Microsoft to export & import Json files.

So, not need to create external solution (eg. DLLs for calling API & parsing received response). API request & response can be done in NAV only using NAV Codeunits & standard .net variables of Windows .net framework & NAV add-ins.

Creating outside solution will require extra maintenance. You need to update your DLL, place DLL in add-in folder & update your NAV codes. Making such solution, you are making customer highly dependent. So, its better to write code natively in NAV for API call & response parsing which can be easily updated & deployed. 

Below are major steps to reuse NAV existing solutions:

Step 1: We have already solution available to prepare JSON structure with required data. We need to reuse this solution to fit into GSP's own schema or Govt. compatible schema. It's easy & quick to modify given Codeunit 16511 or can save in available Codeunit's ID of customer's license with different name. For example Codeunit ID: 50005 Name: e-Invoice Management.

Step 2: Create a Setup table to store GSP's API URLs & Credentials, etc. For example:

Note: You may add/modify filed as per GSP details. Create a corresponding page for this table.

Step 3: Create a log/entry table to store API request & response status & details. For Example: e-Invoice Entry

Note: Above fields are for example only. You may add/modify as per your need. Create a corresponding page for this table.

Step 4: Modify e-Invoice Management codeunit's methos "ExportAsJson(DocumentNo);" to call API & process response. Get the e-Invoice Setup and check if Integration is enabled then Call API otherwise leave the original code to save the JSON file. 

Define the below variables in function "ExportAsJson":

 Update "ExportAsJson" function as below:

 LOCAL PROCEDURE ExportAsJson@1500012(DocumentNo@1500000 : Code[20]);

    VAR

      NewStream@1055602 : InStream;
      HttpWebRequestMgt@1170000000 : Codeunit 1297;
      TempBlob@1170000003 : Record 99008535;
      HTTPStatusCode@1170000002 : DotNet "'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.System.Net.HttpStatusCode";
      ResponseHeader@1170000001 : DotNet "'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.System.Collections.Specialized.NameObjectCollectionBase";
      InStr@1170000004 : InStream;
      Json@1170000005 : Text;
      JSONManagement@1170000006 : Codeunit 5459;
      WasSuccess@1170000007 : Boolean;
      ErrorText@1170000008 : Text;
      TrnsIdentifier@1170000009 : Text[250];

      AckNumber@1170000014 : Text[30];
      AckDateText@1170000015 : Text[30];

      IRNText@1170000010 : Text[250];

      SignedQR@1170000011 : Text;
      SignedInv@1170000012 : Text;     
      eInvoiceEntry@1170000016 : Record 50051;
      OStream@1170000017 : OutStream;
      RequestText@1170000018 : Text;
      QRPayload@1000000001 : Text;
      IRNStatus@1000000002 : Text;
      eInvoiceSetup@1000 : Record 50050;
      AuthToken@1004 : Text[250];
      SuccessText@1000000004 : Text[10];
      QRCodeFileName@1000000005 : Text;
      FileMgmt@1000000006 : Codeunit 419;

                  ArrayString@1000000009 : Text; 

      JObject@1000000008 : DotNet "'Newtonsoft.Json'.Newtonsoft.Json.Linq.JObject";
      JSONArray@1000000007 : DotNet "'Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed'.Newtonsoft.Json.Linq.JArray";
      RequestResponse@1000000010 : BigText;
    BEGIN
      eInvoiceSetup.GET();

               IF eInvoiceSetup."Integration Enabled" THEN BEGIN 

                               

      HttpWebRequestMgt.Initialize(eInvoiceSetup."Base URL" + eInvoiceSetup."

Generate E-Invoice URL");

      HttpWebRequestMgt.DisableUI();

      HttpWebRequestMgt.SetMethod('POST');

                         //Write similar function to get the Auth Token

      HttpWebRequestMgt.AddHeader('Bearer', AuthToken);

      HttpWebRequestMgt.SetContentType('application/json');

      HttpWebRequestMgt.SetReturnType('application/json');

                         RequestText := FORMAT(StringBuilder.ToString); 

      HttpWebRequestMgt.AddBodyAsText(RequestText);

      

      WasSuccess := FALSE;

      ErrorText := '';

      IRNText := '';

      SignedQR := '';

      SignedInv := '';

       AckNumber := '';

      QRPayload := '';

      IRNStatus := '';

      TempBlob.INIT;

      TempBlob.Blob.CREATEINSTREAM(InStr);

      IF HttpWebRequestMgt.GetResponse(InStr,HTTPStatusCode,ResponseHeader) THEN BEGIN

        IF FORMAT(HTTPStatusCode.ToString) IN ['OK','Ok','ok'] THEN

          WasSuccess := TRUE;

          Json := TempBlob.ReadAsText('',TEXTENCODING::UTF8);

          

          JSONManagement.InitializeFromString(Json);

          SuccessText := JSONManagement.GetValue('Success');

          IF UPPERCASE(SuccessText) = 'Y' THEN BEGIN

            AckNumber := JSONManagement.GetValue('AckNo');

            AckDateText := JSONManagement.GetValue('AckDt');

            IRNText := JSONManagement.GetValue('Irn');

            SignedInv := JSONManagement.GetValue('SignedInvoice');

            SignedQR := JSONManagement.GetValue('SignedQRCode');

            IRNStatus := JSONManagement.GetValue('Status');

          END ELSE BEGIN

            JObject := JObject.JObject();

            JSONManagement.GetJSONObject(JObject);

            ArrayString := JObject.SelectToken('ErrorDetails').ToString;

            CLEAR(JSONManagement);

            CLEAR(JObject);

            JObject := JObject.JObject();

            JSONArray := JSONArray.JArray();

            JSONManagement.InitializeCollection(ArrayString);

            JSONManagement.GetJsonArray(JSONArray);

            FOREACH JObject IN  JSONArray DO BEGIN

              ErrorText := JObject.GetValue('error_message').ToString;

            END

          END;

      END ELSE

        SuccessText := 'N';

 

      //Create Entry

      eInvoiceEntry.INIT;

      IF IsInvoice THEN

        eInvoiceEntry."Document Type" := eInvoiceEntry."Document Type"::Invoice

      ELSE

        eInvoiceEntry."Document Type" := eInvoiceEntry."Document Type"::CrMemo;

      eInvoiceEntry."Document No." := DocumentNo;

      

      CLEAR(RequestResponse);

      RequestResponse.ADDTEXT(RequestText);

      eInvoiceEntry."Request JSON".CREATEOUTSTREAM(OStream);

      RequestResponse.WRITE(OStream);

      

      CLEAR(RequestResponse);

      RequestResponse.ADDTEXT(Json);

      eInvoiceEntry."Response JSON".CREATEOUTSTREAM(OStream);

      RequestResponse.WRITE(OStream);

     

      IF NOT eInvoiceEntry.INSERT THEN

        eInvoiceEntry.MODIFY;

     

      IF UPPERCASE(SuccessText) = 'Y' THEN BEGIN

        QRCodeFileName := GetQRCode(SignedQR);

        QRCodeFileName := MoveToMagicPath(QRCodeFileName); // To avoid confirmation dialogue on RTC

        CLEAR(TempBlob);

        FileMgmt.BLOBImport(TempBlob,QRCodeFileName);

        IF TempBlob.Blob.HASVALUE THEN BEGIN

          eInvoiceEntry."QR Code Image" := TempBlob.Blob;

        END;

        eInvoiceEntry.Status := eInvoiceEntry.Status::Generated;

        eInvoiceEntry."Acknowledgment No." := AckNumber;

        eInvoiceEntry."Acknowledgment Date" := AckDateText;

        eInvoiceEntry.IRN := IRNText;

        eInvoiceEntry."IRN Status" := IRNStatus;

        eInvoiceEntry.SignedQRWriteAsText(SignedQR,TEXTENCODING::UTF8);

        eInvoiceEntry.SignedInvWriteAsText(SignedInv,TEXTENCODING::UTF8);

        eInvoiceEntry."QR Code".CREATEOUTSTREAM(OStream,TEXTENCODING::UTF8);

        OStream.WRITETEXT(QRPayload,STRLEN(QRPayload));

      END ELSE BEGIN

        eInvoiceEntry.Status := eInvoiceEntry.Status::Fail;

        eInvoiceEntry."Error Message" := COPYSTR(ErrorText,1,250);

      END;

      eInvoiceEntry.RequestWriteAsText(RequestText,TEXTENCODING::UTF8);

      eInvoiceEntry.ResponseWriteAsText(Json,TEXTENCODING::UTF8);

      eInvoiceEntry."Created By" := USERID;

      eInvoiceEntry."Created Date Time" := CURRENTDATETIME;

      eInvoiceEntryMODIFY;

    END ELSE BEGIN 

                   FileName := DELCHR(FileName,'=','/');

                     ServerFile := FileManagement.ServerTempFileName('.json');

                     IF FILE.EXISTS(ServerFile) THEN

                       ERASE(ServerFile);

                    TempFile.CREATE(ServerFile);

                    TempFile.CREATEOUTSTREAM(OutStrm);

                    OutStrm.WRITETEXT(DN_JSonConvert.Parse(StringBuilder.ToString).ToString);

                    TempFile.CLOSE;

                    LocalFile := FileManagement.SaveFileDialog('Select Folder to Save Json',FileName + '.Json','*.JSON|*.json');

                    IF LocalFile <> '' THEN

FileManagement.DownloadToFile(ServerFile,LocalFile); 

    END;

END;

Note: This code might not run directly, you need to change/update accordingly. Codeunit: Http Web Request Mgt., JSON Management, & File Management are sufficient to call API & easily parse response using few supporting .net variables.

Step 5: Similarly need to write code for cancel IRN. Give a button at e-Invoice Entries page.

Step 6: Finalize your solution by putting required validations to avoid errors. Check the link for validation. 

Happy to help you, pleas comment & give feedback. Or, you may contact us for further detailed information. 

Thanks for reading...