The error "No matching key" when trying to unstake USDC on the BNB chain via Aave could be due to a few common issues. Based on similar discussions, the following steps might help resolve the problem:

1. Update Your Wallet: Ensure your wallet software (e.g., MetaMask) is up-to-date.
2. Check Network Settings: Verify that you are connected to the correct network (BNB Chain).
3. Revoke and Re-approve Token Allowances: Use a tool to revoke and re-approve your USDC allowances for Aave.
4. Sufficient Gas Fees: Ensure you have enough BNB to cover the transaction fees.

Found the answer in the Aave Reddit thread.

The error message "No matching key" commonly arises due to problems associated with the browser or wallet provider's cache. To resolve this issue, clearing the cache and disconnecting, then reconnecting the wallet is usually effective.

Hope that it would help.