validation rule for 2 profile fields

Hi all,

We are consistently getting spam registrations where the same name is entered for first and last name in the user profile.

I'm trying to create a validation rule that would check the first and last name and if it is exactly the same, show the error.

I tried adding a "Match against a field" validation to the First Name field:
Entity type: User
Field name: field_profile_last_name

Reverse - checked

I didn't enter anything for Bundle or Column.

When I added this rule and tried to register, it gives me the error all the time, even if the names are not the same.

Can anyone tell me what I am doing wrong or if there is a better way to ensure the first and last names are not the same ?

Thank you

Terry