[Django]-Django – How to add custom error message in Form?

First you must define a function that begins with clean_[your field name] — for example: def clean_email. Then write your validation in your function and assign an error name and use it in error_messages of your field.

class ValidationForm(forms.Form):
    email = forms.EmailField(label = 'Email', error_messages = {'invalid': 'Your Email Confirmation Not Equal With Your Email'})
    email_confirmation = forms.EmailField(label = 'Email Confirmation')

    def clean_email(self):
       if email != email_confirmation:
          raise ValidationError(self.fields['email'].error_messages['invalid'])
       return email