How do I cancel a transaction?

Market Orders and Crypto Withdrawals
Blockchain operation such as market buy/sell orders and crypto withdrawals cannot be cancelled or removed. Once a transaction has been confirmed by the customer, the process becomes irreversible. This is the direct result of the blockchain technology that Bitcoin and Lykke is built upon, and the process is outside of our control.  

Limit Orders
Once a limit order was already executed, it can no longer be cancelled. Open limit orders on the other hand can be cancelled if the order did not yet match. You may find the related articles how to cancel an OPEN limit order below: