How to fix the «The "autoload" field is not set or empty in the "composer.json" file; please verify the archive.» issue for a Magento Marketplace metapackage?

I have got a response from Magento:

It appears that the issue is with the type field in the composer file.
According to the web page provided, the type is listed as magento2-module instead of metapackage as stated in the documentation.
The reason for autoload error is due to incorrect labeling in the type field.