I'm also not able to link my profile. I do everything right, I tried with an agent on the phone but no luck. From what I understood, it might be because I have a paid representative, but my lawyer doesn't have my application linked and told me to do it if i wanted lol sooo.. maybe other people can't do it because of the same reason..Did you check with the agent whether your photo is uploaded in profile. Then you have GU1.
Linking application is possible if you give place of birth exactly as you have given in you cec profile.
Like I have only my district name, but my wife have district space state.
If you ask agent they will be able to help you linking profile