TOTP app missing from app store

Hi everybody!
I’ve just installed nextcloud 12 and I don’t have TOTP app listed in the app store. It seems to me that all the other apps are there.
When I click on the app link I get this error on the log:

{"reqId":"vHeHhgAGhwR1HT3a1GFf","level":3,"time":"2017-12-24T10:18:34+00:00","remoteAddr":"xx.xx.xx.xx","user":"admin","app":"PHP","method":"GET","url":"\/index.php\/settings\/apps\/list?category=installed","message":"Array to string conversion at \/var\/www\/nextcloud\/lib\/private\/App\/DependencyAnalyzer.php#354","userAgent":"Mozilla\/5.0 (Windows NT 6.3; Win64; x64; rv:57.0) Gecko\/20100101 Firefox\/57.0","version":""}

but I really don’t know what that mean…

What system are you using? Have you installed all required modules?

Also check the admin page if any other error is shown.