Sign in with Layout
Sign in with Layout is one button, in black or white, labelled Continue with Layout or Order with Layout, in three pill sizes and a circle. It sends the person to Layout's approval page, or stays on your screens with a code Layout texts them. The guide covers both, and the button files are ready to download.
Returning people go straight through. A person signed in to Layout who already approved your app is sent back to your redirect URI with a code and sees no page. prompt=consent always shows the page, and prompt=none never does, answering login_required or consent_required instead.
login_hint takes the person's phone number in E.164 and fills it in on Layout's sign-in step. It never sends a code by itself.
Headless verify recognises returning people. verify/start on someone already connected to your app texts a fresh code, and verify with the right code answers the same id. Every verify answer carries id. If the person's Layout account no longer holds the number you provisioned, start answers 409 phone_changed and texts nobody.
The approval page says: “{your app} will be able to place orders for you, paid with the card on file in your Layout account. You can disconnect {your app} anytime in Layout.”
Why it matters
A person can sign in to your app with Layout once and come back on any device without approving again, and a person who changes phones is still the same person to you.
What to do
Nothing, unless you want the button. If your code treated a 409 from verify/start as "already verified", check the code the person reads back instead.
Breaking changes
verify/start answers 200 where it answered 409 already_claimed for a person already connected to your app.