How to order relashionship elements ?

Hello.

In a MB View I use a relashionship :
{% set relationship = attribute( relationships, 'quiz-question' ) %}
{% for post in relationship.to %}

But I would like to change the order to use a custom field. I tried this way :

{% set args = { post_type: 'question', orderby: 'meta_value_num', meta_key: 'question-order', relationship: { id: 'quiz-question', to: post.ID } } %}
{% set questions = mb.get_posts( args ) %}
{% for question in questions %}

Unfortunately it doesn't work at all, nothing appears.
Do you have an idea of what is the best option to do the ordering ?

Thanks.