React-Redux – No reducer provided for key “coins”

Your issue lies with how you’re importing your coins reducer:

import { coins } from './coins'

The latter tries to obtain a named export returned from the file in ./coins.

You are not using any named exports only export default, therefore you just need to import the file as follows:

import coins from './coins';

Using the latter will result with the fact that coins will then contain the value of export default; which will be the coins reducer.