Steam account connection problem

"You cannot add this login method to this account.
You cannot merge two accounts with the same login methods."

I always get this message when I try to link my Steam account to my POE account on the site. Which two accounts? How can I see which two accounts the site is referring to? And how can I fix this? Until Travel to Hideout was the only option on the trade site to get something, it wasn't a problem because I could just send a message and that was it, but now that's the only way to do it, and since the site doesn't recognize that I'm online because I'm not linked to my Steam account, there's nothing I can do.