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.
More details about gas:
Question: How can I fix it?
Answer: You can remedy this by sending 0.01 ETH to that account in order to be able to make the transaction.
A standard Ether transfer TX will be 21000 gas & a gas price of 8 GWEI.
With tokens, the amount of gas is typically 200000 gas, so the total TX fee increases to 0.001 ETH - 0.002 ETH.
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).
Please refer to this article about Binance: https://metamask.zendesk.com/hc/en-us/articles/360049675331-Tokens-not-visible-after-withdrawing-from-Binance