For the WP multisite I have just bought a SSL Alpha Wildcard certificate from Siteground for *.zenblogs.dk.
I have enabled this "define( 'FORCE_SSL_ADMIN', true );" in my wp-config.php
Now when accessing the admin for the main site I can enter the admin area using the protected https, but when accessing the control panel for one of the sub sites I get a "500 Internal Server Error".
This is a link you can see: https://ntgntg.zenblogs.dk/wp-admin/
All DNS is in place after the move to the new IP, which is a static IP address.
There is a user in the zenblogs.dk domain and a user with own mapped domain and it all worked before adding "define( 'FORCE_SSL_ADMIN', true );".
Can you assist?