I'm trying to upload an extension (M1) to Magento Marketplace, but it keeps returning the following error:

The "package.xml" file does not exist; please verify the archive.

I'm not sure what is causing the issue as the package.xml does exist in the root of the folder. To create a tar file, use the cvf command line option (tar -cvzf ...). What am I missing here? Also, is it required to fill out the contents section while compiling the extension package?