To test and debug your Instant Articles before submitting them for review or sharing them with your followers, use the Pages Manager app. If something is wrong, you can then use the article editor to debug them. The article editor can be helpful to highlight errors and warnings in the HTML markup for your content.
Publishers can preview how Instant Articles will look and perform before sharing them with readers. To obtain Pages Manager:
From there, you can preview all Instant Articles associated with your Facebook Page, both published and unpublished. Tap any article to preview and test how the content will appear in Facebook’s mobile app.
Use the Instant Articles editor to review and correct any errors in the markup for specific articles. Access the editor from your Instant Articles production or development article libraries.
From the top of your Page, click Publishing Tools and go to the Instant Articles section in the menu on the left of the screen. Click on Production Articles or Development Articles to open a library. A warning icon appears near the title of any article with errors or warnings.
To review the markup for an article, click on the pencil icon in the Edit column. You can use the editor to review specific errors and warnings displayed at the top of the open article, make alterations to the markup and save the revised version.