Error message: can't add to Watch list

[rachael307]

I keep getting the same error message (with a "trading" number after it???) when I try to add something to my Watch list. It's never happened before, I've not changed anything on my account, I don't have any unpaid items, my notifications are switched on, I've deleted and reinstalled the eBay mobile app, switched my phone off and on, switched the wifi off and on, have not made any changes to my phone or account/bank details etc etc. Can anyone help me out with this? Thanks