add_filter( 'gform_field_validation', function( $result, $value, $form, $field ) { if ( $field->type !== 'address' || ! $field->isRequired ) { return $result; } // .5 = ZIP / Postal Code sub-input if ( empty( trim( $value[ $field->id . '.5' ] ?? '' ) ) ) { $result['is_valid'] = false; $result['message'] = empty( $field->errorMessage ) ? 'Postcode is required.' : $field->errorMessage; } return $result; }, 10, 4 );