JS engine tries to download the required binary file upon plugin activation. If for some reason, the automatic download fails, you can retry downloading the file with `retry` button or you can manually download the file.
Download JS Engine binary zip file manually, extract the content ie: engine file and upload it to js-engine folder in your site’s uploads directory. Usually it is wp-content/uploads/js-engine. Create js-engine folder if not exists.
Final path looks like wp-content/uploads/js-engine/engine
Once the file is uploaded reload the js-engine settings page and make sure that you do not see any error.