When you enter in a domain to crawl, Lumar will automatically test it to see which versions of the site are available. It tests based on two factors: HTTP vs. HTTPS, and with WWW. vs WITHOUT WWW. Lumar will test those four combinations of the domain to see the HTTP responses from those four URLs. 

Ideally, at least one of the URLs will return an HTTP 200 response, meaning that Lumar received a successful response. Make sure to choose any 200 response URL and proceed with the crawl setup.

If there is no 200 level response then there may be an issue, such as a security measure in place blocking Lumar from accessing the site.