I just went to that URL, entered my name and email, and the incentive email showed up immediately. After confirming I got redirected to your website for the sample chapters. So it looks like things are working in general, although perhaps there are some issues with particular email addresses and deliverability there.
Take a look at this troubleshooting help page. If you continue to see problems, you can reach out to ConvertKit's support team at firstname.lastname@example.org (or with the message bubble in the lower right corner) and they may be able to look at the specific email addresses in question to see why there are issues.