Order by meta_value not working

Hi,

I’m trying to order posts by custom field “number_of_plays_sum”.
/api/?json=get_posts&dev=1&custom_fields=number_of_plays_sum&order_by=meta_value&meta_key=number_of_plays_sum&order=desc

This does not work, order_by gets totally ignored.

Am I doing something wrong?

https://www.ads-software.com/plugins/json-api/