I have an original registration form in MemberPress with some custom fields. One of them, is an ID Card. I need to use a custom validation function in my functions.php file to validate this ID Card.
How can I call to this function before submit my form? If it's not a valid ID card, this field will be show like invalid and don't send the form.
I need this to be used with MemberPress forms.
Thank you in advanced!!