Issue with Merchant’s Tab — Couldn’t Add Items (Resolved)

I had a problem with my Merchant’s Tab.
I couldn’t put any items in it — I was able to remove the ones that were already there, but it didn’t allow me to list any new items for sale.

I’m not sure if it was related, but the issue happened right when I tried to add a new item and another player bought something from the tab at the same time.

I managed to fix the problem by changing maps and returning to my hideout.