When it comes to subdomains, the context in which how these subdomains are being used needs to be considered to determine whether a single license applies. If all the subdomains are designed to organize your content within one main site will consider that use as a single end product (thus requiring a single license).
In cases where each subdomain has no relation to each other or the main site and are about different things, then will consider these subdomains different end products regardless of the implementation (single installation). In this case you would need a separate license for each subdomain.
for more clearification please open Help ticket and let them know. Envato Customer support team will be happy to assist you.