My pet is well fed, happy and healed, and yet no matter what I do, I receive the message, "Oh no! None of your pets are eligible for battle. You might want to make sure that they're well fed and happy!"

Help please?

go here tp your stats page, and see if you're in battle. If you are, carry on, or forfeit; and then you'll need to heal again

Thank you so much!

No worries, did that fix it?

Yes, thank you very much for the help. :)