When running truffle-flattener ./contracts/Bridge.sol > Falttened_Bridge.sol .
Getting error as Error: ENOENT: no such file or directory, open ‘c:/Users/raja%20roy/Desktop/XYZ-Bridge/token-bridge/bridge/contracts/zeppelin/token/ERC20/ERC20Detailed.sol’ .
Your path apparently includes a space the the flattener replaces it with %20, which is how spaces are usually handled in URLs but is not the right thing to do in local paths. Workaround - use a path without spaces.