Swap transaction failed "Fail with error 'UNAUTHORIZED'

Hi, I’m relatively new to Metamask. Had previously funded the wallet and successfully staked some ETH with Bancor. Now I’m trying to swap USDC for USDT. I’ve tried 3 different transactions, and on etherscan.io, it fails with Stats: “Fail with error ‘UNAUTHORIZED’” This is quickly becoming an expensive lesson as I’ve already spent about $200 in ETH on these transaction fees. Any ideas what would give me this Unauthorized error on a consistent basis? Like I said, I don’t think any settings on my Metamask account have changed since staking the ETH with Bancor a few days ago. Thank you!