If none of your pets will 'have fun' with a toy even if you buy it and play with them, you're basically just screwed and cannot complete that quest, right?

Basically. But really the reason your pet has no real 'fun' with the toy is because it's fully happy. What you need is a slightly unhappy pet in order to play with it. If your pet has a minion and has had it for a while, it will be fully happy.

removing minions from your pets can help, it takes a few hours for them to show ennui. Ennui happens only if they're not in the Lakeview Resort, which entertains its guests. It is not possible to check out early from there.

Thank you both. :)

I added minions to all my pets a week or so ago to help with the pets page getting messed up and forgot about them.

All my pets are in the lodge and I'm having this problem too, only it's not fixable since you can't take your pets out of the resort.