Discord Nitro is a Discord subscription with perks for your account, but it’s different from a Midjourney subscription. Having Discord Nitro won't give you access to Midjourney, and you don’t need Discord Nitro to use Midjourney.
When you go to the "Subscriptions" page in your Discord user settings, you'll only see Discord Nitro subscriptions. Midjourney subscriptions won’t be listed there. If you accidentally signed up for Discord Nitro thinking it would let you use Midjourney, you might be able to get a refund from Discord.
If you need help subscribing to Midjourney, check out our How to Subscribe article.
To get help with your Discord Nitro subscription, visit Discord's support site.