Hey. Thanks so much for your reply. In my case, the email doesn't contain a UserID, but just my Application Number, like “IRCC Permanent Residence Confirmation Portal - EXXXXXXX”. I don't know why there is a difference - but I think citing the application number should be good as well. Thanks!
Furthermore, regarding the PR card application: I didn't see anywhere mentioning about PR card, but simply that they will mail it to you once they approve the photos/addresses. I don't know what is the exact process of linking the PR card application in GC key (I know how to link an application in GCKey, but I don't know when should I do it, or how do I know if there was already a PR card application for me). Do you know if in your communications with IRCC (emails/letters) did anywhere mention about what we should do about linking the PR card applications? Thanks!