React.Children.only expected to receive a single React element child error
You have a space here:
↓
<Provider store={store}><App /> </Provider>
JSX is kinda picky about spacing on single lines. The above essentially gets interpreted as:
<Provider store={store}><App />{' '}</Provider>
(In fact, Prettier will produce pretty much this exact output)
You can either remove the space:
<Provider store={store}><App /></Provider>
Or break it up on to multiple lines:
<Provider store={store}>
<App />
</Provider>
I had a similar problem and it turns out I had converted my App root from a function to a class, which means I had to change the syntax from this:
ReactDOM.render(
<Provider store={store}>
{ App }
</Provider>,
document.getElementById('root')
);
To this:
ReactDOM.render(
<Provider store={store}>
{ <App /> }
</Provider>,
document.getElementById('root')
);