Correct AWS Policy format for upload.html Remix.js

I'm getting:

Invalid according to Policy: Policy Condition failed: ["starts-with", "$success_action_redirect", "http://"]

in Experiment with the remix.js upload example.

I have filled in the AWS account info in the form with redirect:

http://localhost

And the encoded policy and secret key created via php.

"expiration": "2016-01-01T00:00:00Z",
  "conditions": [ 
    {"bucket": "s3-bucket"}, 
    ["starts-with", "$key", "uploads/"],
    {"acl": "private"},
    {"success_action_redirect": "http://localhost"},
    ["starts-with", "$Content-Type", "audio/mpeg"],
    ["content-length-range", 0, 1048576]
  ]
}

Is my policy incorrect?