In this case, you can consider the fact "How you have configured your website". To determine this, you can browse your website for a while, and check the web address(URL) of a website, whether it stays on with WWW or without the WWW in front of the domain.
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If the address stays with WWW, then your website is configured to work with WWW and SSL should be purchased with WWW. On the other hand, if the address stays without WWW then you should order the SSL without WWW.