How i get WhatsApp abid to compose a message to a specific user in iOS?

Two recent solutions (July 2017)

  1. WhatsApp 'Click to Chat' API feature must work on all devices:

    https://faq.whatsapp.com/en/general/26000030

  2. And, this other schema (for href links) seems to be working also:

    whatsapp://send?text=MESSAGE&phone=+NUMBER&abid=+NUMBER