Hi…,
Welcome.
Make sure you have the latest Fenix version installed.
Please see FAQ - MSFS Importing SimBrief flight plans into the Fenix A320 MCDU
Make sure you have pressed the SimBrief Generate Flight button on the SimBrief webpage.
If still an issue please post the flight plan text string, so we can try to replicate the issue.
Also please advise what steps you have taken with MCDU INIT REQUEST and the results.
Cheers
Ian