What it means
Two-step verification (sometimes 2FA, distinct from authentication templates for end users) is a six-digit PIN you set on your WhatsApp Business number. It is required to register or re-register the number on the WhatsApp Business API, which prevents an attacker (or an ex-employee) from porting the number elsewhere with just SIM-swap access.
Without it, anyone who can receive an SMS on the number can hijack the WhatsApp account. With it, the SMS code alone is not enough; the PIN is also required.
Why it matters
WhatsApp Business numbers are high-value targets. A hijacked number means complete contact-list compromise, ongoing customer-fraud impersonation, and total loss of access to your messaging history. Two-step verification is a single six-digit PIN that closes the most common attack vector.
Treat it like a database password: store it in your password manager, share it with at most one or two senior team members, rotate it when team members leave.
Example
An e-commerce brand fires a customer service lead who had access to the WhatsApp number's SMS-receiving SIM. The next week, the lead attempts to register the number on a new device. SMS code arrives but the registration fails: two-step verification PIN is required, and they do not have it. Attempted hijack thwarted.