React Hook "useEffect" is called in function which is neither a React function component or a custom React Hook function code example

Example 1: React Hook "useState" is called in function "app" which is neither a React function component or a custom React Hook function react-hooks/rules-of-hooks

//Try to capitalize 'app' like
const App = props => {...}

export default App;

Example 2: React Hook "useEffect" is called in function

React component names need to start with a capital letter.
That's because React treats components starting with lowercase letters as DOM tags.

Therefore you should name it "Shoes"