Yes I make money with Whatsapp by direct marketing. First of all you need bulk mobile numbers of the country you would want to market to. Then you use this service here to filter the numbers. They will send the active whatsapp users from the database you provide them. When you receive this active numbers you can then contact them manually and sell your service. Don't spam else Whatsapp will block you.
If you'll try to advertise through WhatsApp you will be blocked soon there. Better try to use Instagram or Twitter for that. If you'll promote your accounts using bots you could even find your targeted audience there.
Never heard that on WhatsApp it was possible to earn well. After all, there is a huge number of other social networks for this. I think that you should switch to something else.
Try another area. There is a very high probability that you can be blocked and all your efforts will be in vain.
I think that making money through WhatsApp is a simple spamming and nothing else. It's not like this only if you want to place your ads there.
I think that if you do advertising in a messenger, then you need to do it in a telegram. because there are more people now.
There's a big risk of being blocked for spamming as the only promotion you can do yourself is mass message sending. You'd better choose another platform for promotion, like Instagram or Twitter.
I agree that you need a lot of time spent with whats app in order to do this. Start with Instagram and niche down into something you are passionate about.