Referencing OpenZeppelin in Solidity Contract, working with Etherscan

Question

I think I am making a simple mistake, but I have been stuck for a while.

I have a simple ERC-20 contract which I have publish on the Ethereum Mainnet and others on Polygon.

This is a sample contract implementation:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.10;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.0.0/contracts/token/ERC20/ERC20.sol";

contract GameCoinX is ERC20 {
    constructor() ERC20("GameCoinX", "GCX") {
        _mint(msg.sender, 150000000 * 10**uint(decimals()));
    }
}

I built, tested, and deployed the code in remix (remix.ethereum.org)

Now, I have successfully created my contract, but I cannot VERIFY my source code on etherscan.io or polygonscan.com. It complains about the reference.

ParserError: Source "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.0.0/contracts/token/ERC20/ERC20.sol" not found: File import callback not supported

Should I put everything in 1 file? How do verify a code file like this on etherscan?

EDIT: How do I get the Standard-Input-Json in Remix?

Answer 1

Should I put everything in 1 file?

Yes, this is the easiest way.