I am looking for freelancer that has done this before with demo to show. We need to see demo and testing to ensure working. We would like to build whats-app bulk marketing web system mainly for blasting whats-app text, image, video and file. IT provide auto whats-app number filtering to ensure active whats-app account and should support virtual number to provide 100% delivery for our users. Our user should be able to login themselves, manage their own blasting, add their own contacts, and so on. How much and how long?