I do not have money for paying for ads, So I decided to go with whatever it is available. I have over 1000 whatsap groups. I would like to send my ads to all groups twice a day without blocking my whatsap. I don't mind using an external software or app. I need to send my ads on my whatsap groups in the morning and evening so that I can get people interested in my service and I can talk to them and try to sell my idea. So I need a reliable solution. What is the safest way to do that?