You can certainly add links to adhoc Zoom meetings onto your Moodle course page, but the plugin, which provides much closer integration, states
"Requires a business or educational Zoom account to configure and setup." So if you don't have one of those, that would be why you are getting an error that says it is only available for a Paid account.
"Requires a business or educational Zoom account to configure and setup." So if you don't have one of those, that would be why you are getting an error that says it is only available for a Paid account.