Validation

Link - docs.microsoft.com/en-us/office/dev/add-ins/testing/troubleshoot-manifest

Office Add-in Validator

This is a command line tool that can be used to validate your manifest.
This uses the same validation service that the Office Store uses.
The feedback you get is the same you would get from submitting

A local copy of the validator is installed when you install Yo Office
Or alternatively just install the validator

npm install -g office-addin-validator 

validate-office-addin manifest.xml 

If the script has been defined in the webpack.config.js file

npm run validate manifest.xml