Solution for error:"PrestaShop\PrestaShop\Core\Domain\Theme\Exception\ThemeConstraintException code 2"
Unzip template. Check any zip file or folder inside if has folder "themes". Copy the template (zip file) from "themes" to your website themes location. Refresh web browser. Go back to office. Click "+add new theme". Go to section "Import from FTP". Select the archive. last step is to "Use this theme". It take some time to finish. It should work. Good luck.