In order for an external link to Facebook to function properly from a Rich Message, the URL must be properly formatted. If the URL is not properly formatted, it can appear that the link is not functioning.
Here is an example of a properly formatted Facebook URL:
The first part of the URL must follow this format, or your link will not function properly:
If you use a URL such as www.facebook.com/events/11111111111/ or https://facebook.com/events/11111111111, the link may not work correctly.