Cookie Error When Logging After Changing Domain

I am using multisite with wordpress. I just changed one of my subdomain sites to it’s own domain and it works… until I try to login. I get this message:

ERROR: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.

I have cookies enabled. I have cleared all cookies. I have searched the wordpress forums and google and have tried many different suggestions and nothing has worked. I have tried adding this code to wp_config.php:
define('COOKIE_DOMAIN', $_SERVER['HTTP_HOST'] );
and got this error message:

The constant “COOKIE_DOMAIN” is defined (probably in wp-config.php). Please remove or comment out that define() line.

I have removed some plugins through the multisite admin plugin page but I can’t do them all without causing issues on multiple websites. Ones I have tried are WP Super Cache and Jetpack.
I can log in to all my other sites, just not this one. I have added a domain to another site in my multisite and had no difficulties.
My website is at https://inspiringfandoms.com. I have created a subscriber account and tried that is still problems. You can try the subscriber account using…
username: auser
password: apassword
I am not sure what else I can do so I am asking for help here.

The page I need help with: [log in to see the link]