How to ge Nuxt.js render csp config to work?

My Nuxt.js app is running in universal mode on localhost:4000 with a backend API that's running on localhost:3000.

I'm adding the following to my nuxt.config.js:

  render: {
    csp: {
      hashAlgorithm: 'sha256',
      addMeta: true,
      policies: {
        'default-src': ["'self'"],
        'script-src': ["'self'"],
        'style-src': ["'self'"],
        'connect-src': ["'self'", 'localhost:3000']
      }
    }
  },

But in Chrome console I get the following errors: