Sadly due to the recent update to Teuxdeux.com service (Neux Teux Deux), TodoToday for TeuxDeux is being discontinued until such time as an updated official (or un-official) API for TeuxDeux is available.
The team behind TeuxDeux have never officially supported an open API for third party applications. TodoToday for TeuxDeux was made possible by the hard work of Jan-Eric Rediger (badboy) who reverse engineered the original TeuxDeux API
https://github.com/badboy/teuxdeux
As TodoToday for TeuxDeux no longer works with the new TeuxDeux service, availability and development is discontinued.
UPDATE: According the the
TeuxDeux FAQ an official API is planned.
No ETA is provided, but when the official API is available TodoToday for TeuxDeux will be updated as quickly as possible.