Validation rules required_if with other condition (Laravel 5.4)

Your rule performs two checks that are independent of one another; just because the external_id field is not required when the type_id != 3, does not mean the integer check is ignored.

What you are looking for is a conditional rule, which gives you finer control of when to perform a check, e.g. :

$validator = Validator::make($data, [
    'type_id'   => 'required|integer'
]);

$validator->sometimes('external_id', 'required|integer', function($input) {
    return $input->type_id == 3;
});

When using form validation, you can access the underlying validator instance by overriding the getValidatorInstance() method:

class StoreRequest extends Request
{
        public function authorize(){
        return true;
        }

        public function rules(){
                return [
                    'type_id'     => 'required|integer'
                ];
        }

        protected function getValidatorInstance() {
            $validator = parent::getValidatorInstance();
            $validator->sometimes('external_id', 'required|integer', function($input) {
                return $input->type_id == 3;
            });
            return $validator;
        }
}

Just came across the same problem and found the following answer that seems to work for me:

issue-using-required-if-validation-rule-in-form-builder

     return [
                'type_id'     => 'required|integer',
                'external_id' => 'required_if:type_id,==,3|nullable|integer',
            ];

Result for me:

field not populated, type id not 3 - pass

field not populated, type id 3 - fail - required field

field populated, type id 3, non-integer - fail in integer rule

field populated, type id 3, integer - pass - all good!

note - think nullable rule came in Laravel 5.3