Getting Invalid Type Error with no Key Path Value
EDIT 

This is a case of staring at your computer for too long. The sections needs to be an array so it should've been 

$this-&gt;addMetadata("links.sections", ["https://news-api.apple.com/sections/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"]);


and not 

$this-&gt;addMetadata("links.sections", "https://news-api.apple.com/sections/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx");