WhatsApp works in almost every market, so the useful question is the short list of places it does not. Unlike SMS, there is no per-country registration to arrange: if the guest can use WhatsApp, you can reach them.
Where WhatsApp does not work
WhatsApp is fully blocked in:
China
North Korea
Syria
Iran
Messages to guests in these countries will not arrive, and there is nothing to configure that changes that.
Blocks are a government decision and they move. Countries have restricted WhatsApp temporarily, and some restrict calling while leaving messaging alone. If you have a significant guest base in a country not on this list but where access is unreliable, plan a fallback channel rather than assuming delivery.
What to use instead
For guests in a blocked country, the practical alternatives are email, which is unaffected, or SMS, which depends on coverage. See SMS country coverage.
Channel preferences let you set which channel a guest is reached on, so a guest in a blocked country can be handled without changing the campaign.
What this does not do
It does not warn you. A message to a guest in a blocked country is not flagged before you send.
Coverage is not the whole story. A guest in a covered country still has to have opted in, and marketing templates are subject to their own delivery limit. See WhatsApp error: "This message was not delivered to maintain a healthy ecosystem".
It does not depend on where your hotel is. The block applies to the guest's location, not yours.
Bookboost cannot work around a national block. It is imposed by the country, not by Meta or by us.
What to do next
If WhatsApp is not connected yet, start with What you need before connecting WhatsApp.
Getting help
Open Help at the bottom of the left menu and choose Talk to Us, or email support@bookboost.io.