I have this problem Problem : Capacity Reached ( My csgo inventory not full , have a lot of keys ) .
MY QUEUED TASKS = Capacity Reached for more than 2 hours .
I'm already have more than keys to trade for Gift ....... My inventory have some cheap gift too + check private inventory + trade offer link + already fillfull all conditions.

This error could appear when the seller's shop is full.

Can you post the URL of the trade here to let me test?

Also, when you make the trade, make sure the Item API is up (the indicator of the main page shows green).