Automating add-in/app installation to SharePoint sites using CSOM

There's no APIs to automate app/add-in installation from SharePoint store. You can only side-load apps/add-ins directly to site. See following blog post for supported capabilities.

• https://blogs.msdn.microsoft.com/vesku/2015/11/20/automating-add-inapp-installation-to-sharepoint-sites-using-csom/ 

Store APIs are currently not in the queue, due license and possible cost impact. There's basically too many scenarios and possible exceptions to cover to automate this with simple API. If this is important capability for you, would suggest to vote following user voice entry and to provide scenario details as a comment to it. 

• https://sharepoint.uservoice.com/forums/329220-sharepoint-dev-platform/suggestions/15147099-adding-apps-from-catalog-or-store-using-csom-api