The user will be redirected to the site home page instead of the intended registration form if you are copying the Registration URL destination link and not the actual Registration URL itself.
If you click or navigate to the Registration URL, you will see that the URL itself actually changes when it gets to its destination. This destination link cannot be used to direct users to a register form.
You must use the exact Registration URL from the Membership Levels. It needs to be copied from the Levels tab exactly as it appears.