In case you want to cancel an ETH transaction before it's mined, you can do that by sending exactly the same transaction with higher fee and 0 ETH as value, to make it easier for our customers we have created such endpoint where you can provide the txHash and password or private key and we take care of canceling it for you.

ETH Mainnet: https://docs.cryptoapis.io/rest-apis/blockchain-as-a-service-apis/eth/index#eth-cancel-transactions