Are you allowed to legally sell a financed phone on eBay?

Hi, I recently sold an iPhone 6s a week ago that I had owed money on from T-Mobile ($240 to be exact) and never paid it off so T-Mobile blacklisted the IMEI. I listed it on eBay and made it very clear in the description as well as title that the phone is blacklisted.

Someone bought it and they said they are gonna use it overseas. But now I'm wondering, could I get in legal trouble for selling this phone since it was technically T-Mobile's, not mine? I mean I see other phones on eBay that are blacklisted so I'm not the only one who sold one like that.

Will this ever come back to me if he decides to use it overseas or is there no possibility of that ever happening?