Orderby Custom Field?

Hello,

We’re trying to use the plugin to order a custom post type generated by a plugin (Event Espresso 4) by a custom field also generated by the plugin. We have no direct access to the custom post type or its predefined metadata key-value pairs because they’re defined somewhere within the plugin, though I’ve been able to extrapolate that the post type slug is

espresso_people'

and the meta-key we want to orderby is

PER_lname’

Organizing the shortcode as

[loop type=”espresso_people” taxonomy=”espresso_people_type” term=”summit-speaker”]

works, however this breaks:

[loop type=”espresso_people” taxonomy=”espresso_people_type” term=”summit-speaker” orderby=”meta_value” key=”PER_lname”]

Any help would be appreciated.

Thanks