Multiple orderby

I am trying to order a filter with multiple fields.

WPQuery supports it.
https://developer.ww.wp.xz.cn/reference/classes/wp_query/#order-orderby-parameters

I have tried orderby='author title'
orderby='author,title'

Neither works.

orderby=author and orderby=title both work on their own.

My overall shortcode is

[mdf_results_by_ajax shortcode="mdf_products per_page=60 columns=3 pagination=tb meta_data_filter_cat=-1 orderby='title'" animate=1 animate_target=body]

Any thoughts?