Two-step verification (2FA) is an optional feature that adds more security to your account. When you have two-step verification enabled, any attempt to verify your phone number on WhatsApp must be accompanied by the six-digit PIN that you created using this feature.
Two-Step verification is a mandatory step to achieve an "Official Business" verification. Refer to the WhatsApp 2FA FAQ for further information.
The Sinch API handles these aspects automatically so there are no tasks required of the client.