GCKEY, for ECAS you don't link anything, you just use the application number, and sponsor details to view an overview of your file.
So for GCKEY linking:
- Choose Application Number and Family Name - Copy/paste application number from email (including the F) and enter PA's last name
- Select one of two options next: Place of Birth or Passport Details
- Fill PA's info for the option you selected above and not both at the same time
- Put the Details of the City where the PA plans to reside after getting PR, this info should match with what you put in form IMM0008
- Put your marital status in.
- Put '2' as the number of members in the application for sponsor + spouse (add +1 per dependents)
- NOTE: Sometimes putting MARITAL STATUS as SINGLE also works.
I found my passport details didn't work, but the Place of birth worked the first time.
If this fails, people have suggested putting a space after your place of birth.