Laravel Solution: Laravelv alidator::validateString|max does not exist Error

In my Laravel 5.6.33 application I need to check dimention of an uploaded file with rule

    'avatar' => [
        'string|max:50',
        Rule::dimensions()->maxWidth(96)->maxHeight(64)->ratio(3 / 2),
    ],

But I got error:

Method Illuminate\Validation\Validator::validateString|max does not exist.

In declarations of rules I added a line:

use Illuminate\Validation\Rule;

But I have the error anyway...

What did I miss ?

Thanks!

Laravel Solution