Yes, it’s possible to cancel a transaction before it gets confirmed by the blockchain by using Zengo’s Stop feature, but this is provided without guarantees of success.
To do so, go to the history tab, then tap a transaction to see its details. If it’s still pending, you should see a Stop button at the bottom of the screen. Tap it to stop the original transaction.
The original transaction should be refunded to your wallet, minus the additional network fees* required for stopping a transaction.
Works for BTC, ETH, and ERC20 tokens (does not work for Polygon). Note that once a transaction has one confirmation on the blockchain, it is no longer possible to stop it.
Canceling transactions on Dapps made via Wallet Connect QR scanner is not supported at the moment.
*Network fees change over time based on network conditions and are not paid to Zengo.