On 28 September 2023 we are making a mandatory change to our REST API. The exchange will reject any request for amend qty up on an already filled GTC/DAY order with the text "Invalid orderID". The change is already accessible in Testnet from 25 September 2023, at 04:00 UTC, and will be live in Production from 28 September 2023, at 04:00 UTC. For more details on the change, please read this announcement: REST API Update: Rejecting qty amend up on already filled GTC/DAY orders.