The registration is "not working" in the sense that we are not receiving the SMS or the call, but the WhatsApp servers give proper answers. When I tried to register the WhatsApp server told me the SMS was sent successfully, but I never received it. If I try to register again it'll ask me to wait 15 minutes.

Then after that it will "work" again once, and then it tells me to wait a whole day.

But we are NOT receiving errors from the WhatsApp servers, and that makes it very difficult to think what could go wrong. I still don't know if it's a problem in the servers or if WhatsApp somehow can distinguish between a legit client registration or Yappari's, and if they were smart enough to give Yappari proper server answers even if it won't work.