Why do transfer fees differ when both are USDT?

USDT can be issued on different blockchains, such as Ethereum and Tron.

ERC-20 USDT uses the Ethereum network and typically requires ETH to pay gas fees.

TRC-20 USDT uses the Tron network and mainly consumes bandwidth and energy. If resources are insufficient, TRX is burned.

Remember: Even though both are USDT, choosing the wrong network could result in the loss of your assets.