Todoist is a Caddi-managed connector. There is no Todoist app to register and nothing for an administrator to configure — you sign in to Todoist and approve Caddi.
Before you start
You'll need:
A Todoist account
A Caddi account
Step 1: Connect your account
In Caddi, open Settings, then Integrations, and go to the My Connections tab.
Find Todoist and click Connect +.
Sign in to Todoist.
Review the permissions Todoist lists and click Agree.
You'll be returned to Caddi with the connection active.
How the connection behaves
Caddi acts as you. The connection reaches the projects you are a member of, including shared ones, at the access you already have.
Access tokens last an hour and are renewed in the background, so the short lifetime is invisible in normal use.
Todoist refresh tokens are strictly single-use. Each renewal returns a replacement and invalidates the one before it. Todoist allows a 60-second grace window for a retry; past that, re-submitting a spent refresh token invalidates every token Todoist has issued for your account and this app. If a renewal fails, Caddi asks you to reconnect.
Troubleshooting
The connection stopped working and will not recover
Most likely an interrupted token renewal. Disconnect and connect again.
A project is invisible to Caddi
You are not a member of it in Todoist. Ask the project owner to share it with you.
Completing or deleting tasks fails
The permissions granted at sign-in were narrower than the loop needs. Disconnect, reconnect, and approve the full request.
An older Todoist connection suddenly asks to be re-authorized
Todoist issued very long-lived tokens with no renewal to older applications. If your connection predates the current flow, reconnect it once when it expires.
Still stuck? Contact Caddi support with the exact error message you're seeing and the time it occurred.
Sources
Todoist API — authorization — Todoist developer docs