Nobody in this forum can look into your account and get the details of this debt.
However, there are no fees for buying on Ebay.
It looks as if you have sold but not for a very long time.
If you have listed anything with an insertion fee or with a reserve, for example, which never sold, or if you did sell something and Ebay refunded on your behalf, you could owe money.
Probably best, if the email you have received is not clear, to contact Ebay for an explanation. Use the link below to get a callback.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)