[WP Multisite] Error When Creating a New *Subdomain* Site

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Please help, I've spent hours reading through support websites and trying various things :expressionless:
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When I go to: Sub.WebsiteExample.com
I get:

Index of /

And when I go to Sub.WebsiteExample.com/wp-admin

I get:
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, webmaster@websiteexample.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request.