Replace "full E.164, e.g. +15551234567" with plain-language guidance mirroring the WhatsApp setup card: "start with + and your country code, no spaces or dashes" plus a worked example. "E.164" is the technical name for the format and means nothing to non-telecom users; the explanation it stands in for is one sentence. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>