Open your browser on your phone.
Go to the seagulls website, not the app.
Sign in and go to tickets.
Click on the season tickets points thing at the bottom.
Click on "season ticket"
Select this season's ticket by ticking the box.
Click on "add to wallet".
Worked for me (and has done in the past) but my brother said it didn't work for him so might not be the solution for everyone.
Just worked for me too. Many thanks.