Will someone please help a noob out & tell me what I am doing wrong here?
It says that "user" is an undeclared identifier.

//SPDX-License-Identifier: Unlicensed
pragma solidity ^0.8.7;

contract UserAccounts {
mapping (address => AccountInfo) public accounts;
uint userCount = 0;

struct AccountInfo {
address user;
bool exists;
}

function accountAlreadyCreated(address user) view internal returns (bool) {
if (accounts[user].exists) {
return true;
} else {
return false;}
}

modifier duplicateDetector() {
require (AccountInfo.user.exists == false, "Wallet address already registered.");
_;
}

function createAccount() public duplicateDetector returns (bool) {
AccountInfo storage id = accounts[user]; <== Error is here.
AccountInfo.id = msg.sender;
userCount += 1;
return true;
}