Where do I put manifest JSON?

Web app manifests are deployed in your HTML pages using a <link> element in the <head> of a document:

<link rel="manifest" href="/manifest.json">                

The .webmanifest extension is specified in the Media type registration section of the specification (the response of the manifest file should return Content-Type: application/manifest+json). Browsers generally support manifests with other appropriate extensions like .json (Content-Type: application/json).

If the manifest requires credentials to fetch, the crossorigin attribute must be set to use-credentials, even if the manifest file is in the same origin as the current page.

<link rel="manifest" href="/app.webmanifest" crossorigin="use-credentials">