I’ve gotten mine working by enabling SSL for Trakt in Mediaportal.
Modify the following file :
C:\ProgramData\Team MediaPortal\MediaPortal\MediaPortal.xml
Search for the following section :
<section name="Trakt">
Within that section, you’ll see the UseSSL entry, which is set to no by default, change it to yes :
<entry name="UseSSL">yes</entry>
You should be able to authorize and sync Trakt from the plugin config.