Question: Why I am getting an "insufficient funds" error?
Answer: This means you do not have enough Ether (ETH) in your account to cover the cost of gas. Each transaction (including token and contract transactions) requires gas and that gas is paid in Ether. You can think of this as a transaction fee. For more on gas, see here.
How can I fix it?
Answer: You can remedy this by sending some ETH to that account, or buying ETH, in order to be able to make the transaction.
Question: Why my confirm button is greyed out?
Answer: On the confirmation screen, you might see the confirm button is greyed out. Please check that you have enough ETH in your account.
Question: My insufficient funds error comes from Binance (BNB).
Answer: If you sent tokens from Binance to your MetaMask on the BSC main network and you meant to send them to Ethereum Mainnet, you will need to send it back to Binance (this will require extra BNB, the native BSC network token to pay for gas; for the details about this please contact Binance Support).
If you have questions relating to Binance or any other sidechain, please read our best practices article on sidechains and custom networks here.