VirtualMachineError: revert at Lottery.endLottery confirmed (reverted)

[dibakarsutradhar]

Error -

Transaction sent: 0xe97361a7db515a30e3feac79b1e14d6e16abd3132949b17a82fbb83cd87bc619
  Gas price: 0.0 gwei   Gas limit: 12000000   Nonce: 7
  Lottery.endLottery confirmed (reverted)   Block: 8   Gas used: 11813033 (98.44%)

  File "brownie/_cli/run.py", line 49, in main
    return_value, frame = run(
  File "brownie/project/scripts.py", line 103, in run
    return_value = f_locals[method_name](*args, **kwargs)
  File "./scripts/deploy_lottery.py", line 55, in main
    end_lottery()
  File "./scripts/deploy_lottery.py", line 45, in end_lottery
    ending_tx = lottery.endLottery({"from": account})
  File "brownie/network/contract.py", line 1693, in __call__
    return self.transact(*args)
  File "brownie/network/contract.py", line 1566, in transact
    return tx["from"].transfer(
  File "brownie/network/account.py", line 680, in transfer
    receipt._raise_if_reverted(exc)
  File "brownie/network/transaction.py", line 420, in _raise_if_reverted
    raise exc._with_attr(
VirtualMachineError: revert
Trace step -1, program counter 2469:
  File "/Users/dibakar/.brownie/packages/smartcontractkit/[email protected]/contracts/src/v0.6/VRFConsumerBase.sol", line 161, in VRFConsumerBase.requestRandomness:    
    function requestRandomness(bytes32 _keyHash, uint256 _fee)
      internal returns (bytes32 requestId)
    {
      LINK.transferAndCall(vrfCoordinator, _fee, abi.encode(_keyHash, USER_SEED_PLACEHOLDER));
      // This is the seed passed to VRFCoordinator. The oracle will mix this with
      // the hash of the block containing this request to obtain the seed/input
      // which is finally passed to the VRF cryptographic machinery.
Terminating local RPC client..

end_lottery() deploy script -

def end_lottery():
    account = get_account()
    lottery = Lottery[-1]
    # fund the contract
    # then end the lottery
    tx = fund_with_link(lottery.address)
    tx.wait(1)
    ending_tx = lottery.endLottery({"from": account})
    ending_tx.wait(1)
    time.sleep(180)
    print(f"{lottery.recentWinner()} is the new winner!")

endLottery() Smart Contract -

function endLottery() public onlyOwner {
        lottery_state = LOTTERY_STATE.CALCULATING_WINNER;
        bytes32 requestId = requestRandomness(keyhash, fee);
        emit RequestedRandomness(requestId);
    }