1 more thing before I head off to bed:

This was in the header of the email that my code was sent from:

Received: from tobias.king-casino.de (tobias.king-casino.de [195.28.12.118]) by mail.[redacted].com with SMTP;
   Thu, 5 Sep 2019 21:18:52 -0400

It looks like you are sending mail from a casino. Might cause an issue sending the codes to some people.

Also, take a look at:

https://mxtoolbox.com/domain/coinsbee.com/

You are not publishing SPF records or doing DMARC might cause an issue sending codes to some people.

-Dave