Error HH8: There's one or more errors in your config file: * Invalid account: #0 for network: sepolia - private key too short, expected 32 bytes

Question

import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox";
require('dotenv').config();

const {API_URL, PRIVATE_KEY} =  process.env;

const config: HardhatUserConfig = {
  solidity: "0.8.19",
  defaultNetwork: "sepolia",
  networks: {
    hardhat: {},
    sepolia: {
      url: `${process.env.API_URL}`,
      accounts: [`0x${process.env.PRIVATE_KEY}`],
    }
  }
};
export default config;

Answer 1

 sepolia: {
  url: `${process.env.API_URL}`,
   accounts: [`0x${process.env.PRIVATE_KEY}`], //No need to concatenate '0x"
}

The issue is from the configuration above. Firstly, there's no need to add the "0x" suffix. Here are a few ways to address the issue (depending on the cause of the problem)

1. If you created the project using creat-react-app, your .env variables ought to be suffixed with "REACT_APP" (see https://create-react-app.dev/docs/adding-custom-environment-variables/)

accounts: [process.env.REACT_APP_PRIVATE_KEY]

2. Else you installed dotenv, use may the following

accounts: [process.env.PRIVATE_KEY]

3. If the above doesn't work. You need to ensure that you are using the right wallet PRIVATE KEY (e.g for metamask see https://support.metamask.io/hc/en-us/articles/360015289632) and not the API KEY from alchemy or infura

I hope this helps. To help others, please do not forget to select this answer as the solution if it addresses this issue. Happy coding