I cannot install the outlook add-in as it keeps putting it in the disabled section and you cannot enable it.
What version of Outlook & Windows are you running? Do you have any security software/plugins that could be causing the issue?
Please try removing the version you have installed 100%, close Outlook, clear the cache for IE and install this updated version. https://d2dq6e731uoz0t.cloudfront.net/27d69392edce0cbd2d7128b9c74d070d/as/OutlookTodoist.Adx.exe