Enter the following into a browser after replacing <domain> with the domain of your site:  

  https://<domain>/index.php/wp-json/wc/v3/

Do you see a big chunk of json that starts with something like {"namespace":"wc\/v3","routes":{"\/wc\/v3":{"namespace":"wc\/v3","methods":["GET"],"endpoints"   or do you get the internal server error?

When entering the information above, I do get this error: 

"There has been a critical error on this website."

So, that tells us that there is a problem with the API layer, either at the WooCommerce or WordPress level.   The first step to try and track this down would be to disable the Atrex - SyncHelper plugin and run the same check again.  

If you see the json response after removing the SyncHelper plugin, that means we've done something in our plugin that isn't working, which needs to be tracked down and fixed.

If you still see the error, then the problem is something in the WooCommerce or Wordpress installation that isn't working correctly, which in turn will prevent our utility from working. Your site admin should be able to view the server logs to see more detail on the error.

Two additional places where you can look to see if there are any obvious issues are available from the main Wordpress admin page. The first is "Tools - Site Health" which has both a status and info page. The status page may show you any critical errors that need to be resolved. The second is "WooCommerce - Status". The first tab shows a lot of information about the WooCommerce status, and should show any obvious errors in the site.