Who you're allowed to message

Having someone's number is not permission to message them. Meta requires opt-in, and the cost of ignoring that lands on your own number.

The rule

Before you start a conversation with someone on WhatsApp, they must have agreed to hear from you there. Specifically, they need to have been told:

That they will receive messages on WhatsApp, and
which business will be sending them — by the name they will see in the chat.

That is the whole requirement. It does not have to be a form, and there is no register to file it with. But you need to be able to point at where the permission came from.

What counts

Any of these is fine, as long as WhatsApp and your business name were both mentioned:

A tick-box at checkout, on a booking form or on a sign-up page.
Someone messaging you first — the strongest form there is.
A click-to-chat link or QR code they chose to use.
An opt-in page they filled in.
A written or verbal agreement in person or over the phone, if you record that it happened.

What does not count

A number in your billing system because they once bought something.
A list bought, scraped or swapped with another business.
Numbers from a competition, unless entering plainly said you would message them on WhatsApp.
Permission for email or SMS. Channel-specific — WhatsApp has to be named.

This is enforced by your customers, not by paperwork

Nobody audits your opt-in records. What happens instead is that people who did not expect you press Block or Report. Enough of that and Meta cuts your messaging limit or restricts the number. See Messaging limits and quality rating.

How Wap2b handles it

Every contact carries an opt-in status, and broadcasts only go to contacts marked as opted in. Opted-out contacts are skipped silently — they are not counted, not charged and not messaged.

You can set the status when adding a contact, set it in bulk when importing, and filter your contact list by it.

Replying to someone inside an open conversation is not affected by any of this. If they messaged you, you may answer.

Handling opt-outs

When someone asks to stop hearing from you, act on it:

Find them in Contacts.
Set them to opted out.

They stay in your list, and you can still reply if they message you again — they just drop out of every broadcast.

Make it easy to leave

Adding a "Reply STOP to unsubscribe" line to marketing templates costs you almost nothing and is far better than the alternative, which is a block. A block is invisible to you and counts against your number.

Good practice worth the effort

Say what they are signing up for. "Order updates" and "weekly offers" are different promises; people who got the second when they expected the first are the ones who block.
Message soon after opt-in. Permission goes stale. Someone who opted in eight months ago has forgotten you.
Keep marketing infrequent. Frequency drives blocks more than content does.
Prune the silent ones. Contacts who never once replied are your riskiest audience, not your biggest opportunity.