Hmmm~ I’m going to assume you checked your spam folder? Sometimes a site doesn’t send codes right that second, so I’d be patient for another 15-30 minutes.
When you’re not logged in and on their main page that I linked to, there seems to be a “contact” link at the very bottom. Try using that to shoot them a message about it if your code doesn’t come in soon.
Or you can also post a comment in the BunPro thread that the site’s creators have here on WaniKani and wait for them to get back to you here.