Can you log into your PM account and just check your have the 3 yr sub added to it? It should say you have so many days left (over 1000).
All I did was go to the Accounts section in the settings of Syncler, under Debrid Services you should see Premiumize, click on that and it gives you a code which you have to add to premiumize.me/device and click done.
See instructions here for adding RD but change to Premiumize How To Install & Use Syncler on Firestick/Android TV (2024)