What does the 'Insufficient Funds' error on Binance mean, even when I believe I have enough crypto?

'Insufficient Funds' doesn't always mean you lack the crypto itself. It can also mean you don't have enough BNB (or the relevant trading fee token) to cover the trading fees. Binance charges fees, and using BNB often provides a discount. Also, ensure you're using the correct wallet/account and that the crypto is actually available for trading (not locked in savings or futures).