There are two situations when wanting to add a "Book an appointment" button on WordPress:
1. If you've had your website built by an agency or you are hosting your WordPress website, please refer to this article.
2. If you've built your website yourself using https://wordpress.com,
WordPress puts restrictions on external companies. In this case, our clients add an image that looks like a button and put the URL of their GOrendezvous home page.
Here is an example from one of our clients: NXT GEN Physio
Here are the steps to follow to create your GOrendezvous home page: https://gorendezvoushelp.helpscoutdocs.com/article/66-create-your-gorendezvous-homepage