Https only not working

[ricardolpd]

We are currently attempting to use the https_only flag and for we created a static.json as per the docs in the root of application, however when we use an http url, there is no redirection to https, we can see the correct static.json inside the instance within /app/static.json and the logs state that it is using the provided static.json

We also attempted several changes

{
  "root": "build/",
  "routes": {
    "/**": "index.html"
  },
  "https_only": true,
  "headers": {
    "/**": {
      "Strict-Transport-Security": "max-age=31557600"
    }
  }
}

Our Procfile is as follows:

web: npm run start-prod

Our package.json

"scripts": {
    "changelog-lint": "node ./scripts/changelogLint.js",
    "start-prod": "node server.js",
    "start": "react-scripts start",
}

Could you provide some clues on how to debug this? Is it possible to check what config was used within nginx.conf?