To add the standard PromoteMyPlace availability calendar to your website, the standard availability page needs to be added.
To add this page, go to Website Basics > Website Pages.
Click Add New Page and select the check box next the Availability page.
Then go to Edit Website Content > Availability and make sure that the box that says ‘Use third party availability calendar’ is not ticked.
Please see here for instructions on how to update the availability calendar.