Thanks for your help that worked! And having added it to my account on the website, it also shows on my app.
Shame the Tfl phone line couldn’t suggest that. Checking online, all my previous journey data is correct, so I don’t know why it failed the checks.
Interestingly, the journey I made into London on the same day I got the railcard added hasn’t been discounted, but the journey home has.
Thanks for your help