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"