The web manifest is a simple JSON document, but it's easy to make typos or forget things. If your site is not properly registering the manifest file, you will need to troubleshoot the issue. Fortunately, there are a few resources to help you validate your file.
Google hosts a simple online validator (https://manifest-validator.appspot.com) where you can enter either a URL or just paste the manifest code into the page. It will parse your manifest and let you know if there is an issue:
The nodejs Web Manifest Validator (https://github.com/san650/web-app-manifest-validator) is a module you can include in your automated testing workflow to validate a manifest file. It is a couple of years old, so you may need to fork the project and update it if you are using newer manifest features. Remember that the manifest specification is not final and can...