When using Safari on a Mac, the browser may automatically extract that zip file that i needed for installation of the plugin. You’ll know this happened because you’ll see a regular folder in place of a zip file.
If possible, try downloading the file with a different browser, such as Firefox or Chrome.
Alternatively, you can disable the auto-unzip in the Safari preferences:
Safari -> Preferences -> General, then uncheck the “Open safe files” option.
Now, please re-download the file and once the download is complete, you will then have the proper format to add into Wordpress (‘.zip’ extension).