Adding additional validation rules to forms

[eluser]transition[/eluser]
So i have a form that uses the standard form validation class and that works just fine. Once the form is validated i use the data to call an API. I'm trying to make sure if that API call fails that my form returns back re-populated with the error message. Any suggestions on how i can somehow include this API call as a part of the form validation?

[eluser]transition[/eluser]
Is this really a dumb question or does know one know?

[eluser]mmiranda[/eluser]
you should try callback functions, its all explained in the userguide