Error: "Unable to locate this TxnHash"

This error arises when a transaction is stuck locally, and has not been properly submitted to the blockchain.

Your first step should be to access the block explorer and establish whether or not your transaction has actually been posted. Make sure you're accessing the relevant block explorer for the network you're using -- for example, Etherscan for Ethereum, or BscScan for BSC. Inputting your public address on the block explorer will allow you to review all your past and pending transactions.

Then:

1. Look for the transaction in question. If not easily identifiable by timestamp and token quantity, you could try cross-referencing against the transaction ID (find out how to locate this here) or inputting it into the block explorer's search bar.

2. If your transaction is visible on the block explorer, either wait for it to complete, speed it up, or cancel it.

3. If your transaction is not visible on the block explorer, but is still showing as pending in MetaMask, you should first try restarting your browser. This can sometimes clear your transaction queue. If this doesn't work, you may need to reset your wallet.

Find out how to reset your wallet here.

Before you do so, make sure you have your Secret Recovery Phrase (seed phrase), password, and private keys (imported accounts) backed up and secure.

Resetting your wallet will not result in you losing any funds. It will, however, clear your transaction history (although this will still be visible on a block explorer).