Uniswap query lookup

When the code reaches getPairsByIndexRange, I am getting the following error:
Error: Transaction reverted: function call to a non-contract account

I tried copying the same UniswapQuery code from Etherscan and pasting into my VSCode and running it as a separate contract and test with Hardhat but still getting the same error. But when I enter the 3 parameters in the Read Contract section on Etherscan I successfully get all the pairs.

Does this code from the repo only work on Mainnet or Mainnet-fork? Or should it still work on localhost (for example npx hardhat node)?

With the environment variable what does the Readme note below mean:
ETHEREUM_RPC_URL - Ethereum RPC endpoint. Can not be the same as FLASHBOTS_RPC_URL

I am using localhost:8545 as the ETHEREUM_RPC_URL (through npx hardhat node). But what is FLASHBOTS_RPC_URL? There is no such environment variable inside the code.

Start at getPairsByIndexRange and review the README's ETHEREUM_RPC_URL and FLASHBOTS_RPC_URL notes. Reproduce the call with the Hardhat localhost setup and compare it with the successful Etherscan Read Contract call; done means the required network and RPC configuration is documented or the error is resolved.

Written by the indexing model from the issue text.