It is not just fitbit, even if your PayPal account is limited, eBay won't let you sell product. You will face this problem in future, you have to take care of few things here.
Make assure you login in eBay & Paypal with same IP, list only those products which you have, don't cancel orders on daily basis, never ever cancel any transaction through Paypal while eBay is not giving you option for refund.
I hope this information will help you in future. Don't worry, there are millions way to show them that you are owing items.
Relax about it