Protect sub sites in Wordpress Multisite Set up

Hi There,

I was advised to use URL groups to protect sub sites in a Wordpress Multisite set up.

However, I have tried this and I cannot get it to work.

My Main site has the Membership plugin enabled.

domain.com

The url group I set up is

support.domain.com/.+

However, this does not seem to work.

Please could you let me know what I'm doing wrong?

Thanks,
Michael