Laravel Backpack not uploading image

I am attempting to upload a file (country flag) to a simple table countries which should be saved in a "flags" folder of public.

In my add field declaration I have

$this->crud->addField([ // image
          'label' => "flag",
          'name' => "flag",
          'type' => 'image',
          'upload' => true,
          'disk' => 'flags', // in case you need to show images from a different disk
          'prefix' => 'flags/'

and in the filesystems file I have:

'flags' => [
        'driver' => 'local',
        'root' => public_path('flags'),
        'url' => '/flags',
        'visibility' => 'public',
    ],

When I upload it tells me that the field is too short (it is varchar 255) as it seems to want to store the file as data image.

via Chebli Mohamed