AR750S (Slate) - MAC Clone Help

I am trying to enter a MAC clone address because our internet provider isn’t allowing a router to connect. When in the web software all the buttons on the left side work, except the MAC clone. Is there a procedure that I am not following?

You may need to have a check of ttl

Got my issue sorted out, and can now access the MAC clone feature. But it won’t let me create a MAC address.