The phrase "separate subscription" means having a different or independent payment plan or membership for a specific service or product, typically different from your main subscription. Full definition
Some channels that usually require separate subscriptions now come included with the base TV package. (creditdonkey.com)
Unfortunately, e-magazines and other digital content (like newspapers) are crippled by publishers» insistence on overcharging for them: while customers understand that digital distribution costs less than physical and want to buy content once and read it online, on a Nook Color, and on an iPad, publishers insist on charging separate subscriptions for print, online, and iPad or Nook Color subscriptions. (davidderrico.com)
One thing that gamers need to keep in mind is that Sony actually offers two separate subscription services for PlayStation owners. (techtimes.com)