There's a few reasons something like this can happen. Here's a quick list of things to check for:
Subscription purchased through the iOS app
If you purchased your subscription through the iOS app and it's not showing up in your account, try going to the main menu of the Brilliant app and tapping the "restore subscription" button. Your subscription should be added back to your account in a few minutes, though it may be a good idea to restart the app, just for good measure. If this doesn't work, there's a few other things to check.
Subscription missing due to Multiple accounts
If your subscription is missing and you didn't purchase it through the iOS app, this usually means you accidentally created two different Brilliant.org accounts. Perhaps one with your email, and another via the login with Google or Facebook workflows. You can learn how to diagnose this issue, close one of your accounts, change your email address on your account, and make other account changes here.
Subscription missing due to an underlying payment issue
Occasionally, this can also be caused by an issue with your underlying payment provider (PayPal, credit card, etc.). If you're certain that you have only one Brilliant account and that you should still have access to Premium, please reach out to us with the email address associated with your Brilliant account at firstname.lastname@example.org. We'll be able to get back to you much faster if you can associate the purchase receipt or transaction ID with your email.