This is a complex action. My guess is that you'd be better off if you link to a 3rd-party site to handle this.
E.g., the actions are different if the end-user has Gmail vs. Outlook.
This post includes creating URLs for specific email providers, and a free 3rd-party service that will handle them all:https://stackoverflow.com/questions/5831877/how-do-i-create-a-link-to-add-an-entry-to-a-calendar