A shared space starts with an invitation. Tell your partner what you would like to use Tiptoe for before you send the link. “Could we keep the grocery list here?” is a perfectly good beginning.
Open the invitation screen in your shared space. Send an email invitation or copy the link and share it yourself. Your partner should use their own account, not your sign-in details. Never forward a verification code or share a password to help someone join.
An invitation connects two accounts to one shared space. One subscription covers both partners, so your partner does not need to buy a second plan. If the app says you are already covered, continue with that access.
If a link has expired, create a fresh invitation. If it has already been used, ask your partner to sign in with the account they joined with. A space can have two people; check your account if you see a message that it is full.
There is no rush. Keep using your tasks and lists while you decide together what belongs in your shared space.