I am full web stack developer I can build web application for GST billing (Like BusyWin and Marg but it is on web) with all features like sale invoice, purchase invoice accounting, print invoices etc with Front to Back End, new responsive design( no template), CMS, with all dynamic pages with these languages HTML5, CSS3, PHP 7, MySQL, JSON, XML Javascript etc. We assure you that we will satisfy you. If you would not satisfied with our work we will make one more design for you as you think or like. It is our guarantee. Please discuss with me more on chat window.