Background Processing error

I am trying to use Square as my system of record for all of my products (we have about 18000) and when I try to sync all the products from Square to Woocommerce, it only imported 500 of them and then I get the error message that says:

“WooCommerce Square: It looks like your site does not support background processing, which means large numbers of products may not sync successfully with Square. Read more here on how to resolve this.”

I did the test when you follow this URL:
http://cje.d74.myftpupload.com//wp-admin/admin-ajax.php?action=wc_square_background_sync_test
and I got 0 as a result.

What do I need to do so that all of my products can sync in the background?