Form input validation

Guys need a help

I’m wondering if it’s possible to setup a contact form that can let a user know if they have entered the wrong information.

I’m building a gift certificate form, and it needs to be able to tell the user if they inputed a correct gift certificate code. So I would need a way to tell the system what is correct and what isn’t. Any way to handle this? If not, are there any third party embed’s you can recommend?