Sounds like there is a broken link in the sidebar event. I will look into that. In the meantime, this is the correct link to the page where you can change your pet's name: https://subeta.net/pets.php

(Click the arrow next to the pet and there is an option "Change name")

Welcome back to the site :)

Just fixed the broken link. (This fix isn't retroactive, so your sidebar event still has the wrong link and I won't be able to fix that one unfortunately. But any new sidebar events sent from here on out will no longer have this problem. Thank you for bringing it to our attention!)