wpmu_welcome_notification not in HTML

Hi,

I am working on a WordPress network and made a nice template for my emails. Unfortunatly the email send from hook wpmu_welcome_notification is not working. Can someone help me figure this out?

This is the mail i am talking about:

Your new SITE_NAME site has been successfully set up at:
BLOG_URL

You can log in to the administrator account with the following information:
Username: USERNAME
Password: PASSWORD
Log in here: BLOG_URLwp-login.php

We hope you enjoy your new site. Thanks!

–The Team @ SITE_NAME’ );

https://wordpress.org/plugins/wp-better-emails/