Before sending the request on the block chain, you will be asked to Confirm on your wallet, and an Estimated gas fee will be provided at this stage. You are recommended to maintain the BNB balance in your wallet to be at least 50% more than the estimated fee. This would prevent the chance of transaction failed due to run out of gas fee. For example, if the estimated gas fee is BNB0.001, you are recommended to have at least BNB0.0015 in the wallet at the point when you confirm the transaction.