The issue that your clients are reporting with the Bulk Product Sync plugin is likely caused by an invalid JSON response from the server. When the server returns an HTML response instead of a JSON response, the browser will throw an error that looks like “Unexpected token ‘<', " Permalinks in your WordPress admin panel, and select the “Post name” option. This will ensure that your site’s URLs are structured correctly, and should resolve the JSON parsing error that your clients are seeing with the Bulk Product Sync plugin.
Once you have updated your permalink settings, you should test the Bulk Product Sync plugin again to confirm that the issue has been resolved. If you continue to experience issues, you may need to consult with a developer or contact the plugin’s support team for further assistance.