Signing and Verifying Arbitrary Data

I tired authentication user by blockto.
i have done the signing successfully but on the verify step serve seems the problem as far as i see is cros https://testnet-faucet.onflow.org/fund-account/flow.access.AccessAPI/GetAccountAtLatestBlock
Can anyone help me to solve this problem?

Can you share more about what you are doing and what the error is?