Step 1 - Writing the contract

// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.13;

contract StakingContract {
    uint256 public totalStaked;
    mapping(address => uint256) public stakedBalances;

    function stake(uint256 amount) public payable {
        require(amount > 0, "Amount must be greater than 0");
        require(msg.value == amount, "Amount must be equal to msg.value");
        totalStaked += amount;
        stakedBalances[msg.sender] += amount;
    }

    function unstake(uint256 amount) public payable {
        require(amount <= stakedBalances[msg.sender], "Not enough balance");
        totalStaked -= amount;
        stakedBalances[msg.sender] -= amount;
        payable(msg.sender).transfer(amount);
    }
}

https://sepolia.etherscan.io/tx/0x897ada77f33c0b76a16cf996b21c74f28d2702f8c8141ca8607ce4a53e7d53aa

ABI

[
  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "amount",
        "type": "uint256"
      }
    ],
    "name": "stake",
    "outputs": [],
    "stateMutability": "payable",
    "type": "function"
  },
  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "amount",
        "type": "uint256"
      }
    ],
    "name": "unstake",
    "outputs": [],
    "stateMutability": "payable",
    "type": "function"
  },
  {
    "inputs": [
      {
        "internalType": "address",
        "name": "",
        "type": "address"
      }
    ],
    "name": "stakedBalances",
    "outputs": [
      {
        "internalType": "uint256",
        "name": "",
        "type": "uint256"
      }
    ],
    "stateMutability": "view",
    "type": "function"
  },
  {
    "inputs": [],
    "name": "totalStaked",
    "outputs": [
      {
        "internalType": "uint256",
        "name": "",
        "type": "uint256"
      }
    ],
    "stateMutability": "view",
    "type": "function"
  }
]