How much is the processing fee for BitPay?

I'm curious about the processing fee for BitPay. Could you please clarify how much it costs to use this service for transactions? Is there a fixed fee or does it vary based on the amount of the transaction? Additionally, are there any hidden costs or fees that I should be aware of when using BitPay? It would be helpful to understand the full cost structure before deciding to use this service for my cryptocurrency transactions.