Please tell me - where did you get the app? Our official apps never prompt for any redemption codes.
If you've had such code and redeemed it manually in the past, then it indeed can't be redeemed there a second time. According to our database, your account is Premium until October 2nd, 2014 so all you need to do is to us the same login credentials to access it.
Or do you have a new redemption code for another year of Premium and it won't work on the redemption page?
Thank you for your quick response.
I thought I had to install something, but I just went to Todoist.com and
logged in with my credentials, and I'm in. Sorry for the false alarm.