If the embedding is not showing up, chances are that you are running your website directly from your local computer's file system.
Probably the fastest way to fire up a super basic webserver is to use PHP from the command line. It serves up the current directory at localhost:8080.
php -S localhost:8080 .
In other words, the address showing up in your browser needs to start with either http or https, and not with file.
You can also host your website online to test our embeddings. Here are a couple of options: