See it work
Five pilgrims, five ways of writing a number
The register at a Kushinagar guest house fills with numbers from Thailand, Myanmar, Vietnam and India, each written the way its owner dials at home. Pick one to see what WhatsApp needs instead.
The second sample is the one that causes trouble. A Thai pilgrim writes their mobile number as they would at home, with a 0 and no country code, and the register cannot tell it from an Indian landline. Ask for the number with its country code at the desk, or have the pilgrim message your number first, so WhatsApp hands you the full number itself.
Clean numbers matter twice in Kushinagar. A booking confirmation that never arrives means a group waiting at Gorakhpur station with no pickup, and Meta charges each message by the recipient's country code, so a number stored as Indian when it is Vietnamese is billed and delivered wrongly.