Support
There is no account and no login, so most of what usually goes wrong cannot. Here is the rest.
Pairing two phones
Both of you need an iPhone. Pairing rides on iCloud, so both phones need to be signed in to iCloud with iCloud Drive turned on. One of you sends the invite from More, the other opens the link. If the link arrives before the app has been set up, the app will ask you to answer the door first, name the person, and then open the link once more. Tapping the same link again is always safe.
A note seems slow to arrive
Notes are delivered quietly in the background, and iOS decides the timing of quiet things. Opening the app always checks for anything waiting. A note written offline is kept safely and crosses when the connection returns. Nothing is ever lost in between.
A knock when a note arrives
Lintel is silent until you ask it not to be. In a room made for two, More has a switch under When a note arrives. Turn it on and a note from the other phone brings one line to your Lock Screen: Something is waiting under today's card. Never the note, never a name. If you said no when iOS asked, turn notifications on for Lintel in Settings.
The same card, on both phones
A new pairing takes effect at the next midnight, so nobody's card changes in the middle of a day. From the first shared morning on, you are dealt the same card. If your phones sit in different time zones, the room follows one shared day boundary, set when the pairing was made.
The widget
Add the Lintel widget from the Lock Screen or Home Screen editor and today's card is simply there. It updates when the day turns.
A new phone
Restore the new phone from your iCloud backup and everything is where it was. Set it up fresh instead, and your notes come back once you sign in to the same Apple Account and open the room. If you bought the house, More has a line to restore it.
Sound
Sound is off until you turn it on in More, plays only inside a room, and never overrides your ringer switch. If the phone is silenced, Lintel is silent.
Taking things back
Remove the keying, unpair, or delete the app at any time; the privacy page says exactly what each one does and what it removes.
Anything else
Write to hello@meetlintel.com and a person will answer, usually within a day or two.