Formatting cells for social security #'s

Hello -

I'm trying to create a column(F) in which the user would need to enter their 9 digit social security number without dashes. Therefore if they enter a dash, or don't enter the full 9 digits they should be prompted to do so with a pop up. I tried data validation and entered the following

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this doesn't seem to work b/c if I enter just the 9 digits I still get an error notification.

Any help is greatly appreciated