My active pet is fed and happy, but it says none of my pets is elegible.

Maybe it's stuck in another battle? You can check it here!

In addition to needing to be fed and happy, you also need to make sure that your pet isn't at zero health and that they aren't already in a battle. You can check if your pet is stuck in a battle on this page.

you can also heal your pet HERE if it's at 0 hp

Thank you all, I was stuck in a battle.