I don’t trade often but I don’t remember seeing this error come up before when I did.
I looked around in popular trading discords like Rolimon’s and from what I could see, numerous people were experiencing it today, then before that people were talking about it in February, then before that in May of 2020.
I think this has to do with the trade inbound API being throttled as Roblox recently implemented a stricter limit. Are you using any extensions such as Roblox+ that retrieve your inbound trades repeatedly in a short amount of time?