Schema App's Crawler and Highlighter Tool renders a web page in a Chromium-based web-driver to allow us to render JavaScript before processing. Some IT firewalls may block these requests by default or under other circumstances. By whitelisting our web-driver's IP (52.45.62.191) it would allow us to view the webpage as intended and create the schema markup for the different elements on the page.
In some cases, whitelisting the IP is not available, so you could secondarily use the Schema App User-Agent.
Mozilla/5.0 (compatible; SchemaBot/1.2; +https://www.schemaapp.com/bot/)