Redirection error “This feature is not enabled.”

I am trying to use this plugin to redirect the domain “americanspies.com” (in any iteration) to a page within my WordPress site at https://granick.com/american-spies-the-book/

However, no matter what I try, the browser resolves to https://granick.com/wp-signup.php?new=americanspies.com and displays the error “This feature is not enabled.”

What am I doing wrong?

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