add_filter( 'frm_fields_to_validate', 'skip_validation_for_a_specific_field', 10, 2 );
function skip_validation_for_a_specific_field( $fields, $args ) {
	$target_form_id = 220; // change 220 to the ID of the form
	if ( $target_form_id === (int) $args['values']['form_id'] ) {
		$field_id_to_remove = 1204; // change 1204 to the ID of the field to skip
		foreach ( $fields as $key => $field ) {
			if ( $field_id_to_remove === (int) $field->id ) {
				unset( $fields[ $key ] );
				break;
			}
		}
	}
	return $fields;
}