A phone number has to be valid before Bookboost will send an SMS or WhatsApp message to it. If a guest is not receiving those, an invalid number is the usual reason, and this explains what makes one invalid.
Bookboost does not decide this itself. Validation is done by libphonenumber, the same open-source library most systems use, so a number Bookboost rejects would be rejected almost anywhere.
How a number is checked
Two passes, in order.
The number as written. It is checked exactly as it arrived, for example 015223433253. If that passes, it is valid and nothing else happens.
The number plus a country code. If the first pass fails, Bookboost adds a country code taken from the guest's address, for example DE for Germany, and tries again.
If the guest has no address on file, the second pass cannot happen and the number is marked invalid. This is the most common cause: a local-format number with no address to infer the country from.
Leading zeros
A number beginning 00 is read as a +.
00660891234567 is valid, and means +660891234567.
0660891234567 is invalid.
000660891234567 is invalid.
Bookboost also tidies the number before checking it, so a repeated country code such as "+66 +66 0891234567" is reduced to one before validation rather than failing on the duplication.
Fixing an invalid number
Store numbers in international format. A number written as +49 15223433253 validates regardless of what else is on the profile. This is the reliable fix.
Add the guest's address so the country can be inferred for local-format numbers.
Correct it at source. If the number is synced from your PMS, fix it there. See Editing a guest profile for which fields you can change in Bookboost.
What this does not do
Valid does not mean real. Validation checks that the number is correctly formed for its country, not that anyone answers it.
It does not tell you whether the number takes WhatsApp. A valid mobile number may have no WhatsApp account behind it.
Bookboost cannot override the result. The library decides, and support cannot mark a rejected number as valid.
It does not check landlines against SMS. A valid landline number is still a landline, and an SMS to it will not arrive.
What to do next
To find every guest you cannot currently reach, build an audience with the Reachable filter set to exclude. See Audience filters: reachability.
Getting help
Open Help at the bottom of the left menu and choose Talk to Us, or email support@bookboost.io.