A red cross on API data on the Verify integration page implies that the request was unable to reach ShieldSquare instance. Ensure by verifying the following.
You should be using Sandbox ID when verifying integration. When you use Production ID, Verify Integration page does not work.
If any proxy or CDN is employed in front of your server, check if async is supported by them. If not, alter _async_http_post as false in the ss2_config file.
The current version of the PHP connector will not support Async data post when hosted on the Windows server.