There are different reasons why you might be experiencing this:

• Your metal is not tradable or not craftable, you need clean metal in order to trade with our bots. You can check this at your steam inventory
• Your or the bots backpack is full and cannot carry any more items.
• The bots are experiencing some connection issues.
• You are being affected by trade holds.
• Strange Banking:
  • The bots already have 15 units of the strange you are trying to sell. The error "You offered no valid items" is caused by such stock limit
  • The strange that you are trying to sell is not craftable (check if we are accepting that version) or not tradeable.
• Killstreak Kit Banking:
  • "You offered no valid items" means that we already have hit the stock limit for the kits you are trying to sell. The current stock limit is: 5 of the same basic kits and 1 of the same specialized and professional.
• MvM Part Swap:
  • The parts that you are trying to sell are currently not being bought. For example: If it says "Reinforced: 0/0.05" then it means that we aren't buying reinforced parts at that moment.
  • If the price of the parts you are trying to sell is lower than 1 scrap, you have to sell multiple parts in order to get at least a scrap. For example, if we pay 0.5 scrap for Reinforced parts, you need to sell 2 of these parts, since the bots cannot pay you less than 1 scrap.