I notice in this discussion that the lots of people (2018 through present at least) aren't getting email from this developer. That happened to me too this morning when I went to buy this addon and had to sign up on his site.
The problem appears to be that his site is sending email claiming to be from noreply.nobita.me, and such subdomain doesn't exist. More and more modern mail server configurations automatically discard all such bogus email from fake domains. I didn't get a signup confirmation email, so I decided to look at our server logs and noticed the problem. Using a fake domain might have been ok in 2010 (or 2000), but not in 2020. We were a late adopter to reject mail from bogus domains, and the day we did, it's amazing how much spam disappeared (we still get a lot, but a lot less). By the way, he is using mailgun.net to send email and I'm really surprised a commercial email provider would even allow itself to send email claiming to be from a non-existent domain.