I didn't receive a zip file
If you download your purchase with the Safari web browser you may not see a .zip file, and may instead see a folder called "Laguna" that has a bunch of files inside of it, like the screenshot bellow.
If this is what you see, your Safari is automatically unzipping the file and you'll need to update a setting inside of Safari so it downloads the file properly.
1. Open Safari and go into the Preferences
2. Locate the setting "Open 'safe' files after downloading"
3. Uncheck that option
Now redownload the Laguna theme file and you will have the .zip file that you need to install the theme to WordPress