The credit will be applied to your account, and you can activate Premium from there. Common Troubleshooting
: Once your payment is confirmed, go back to your Spotify app. If it hasn't updated yet, close the app completely and reopen it. You should now see the "Premium" badge in your settings! Alternative: Using a Gift Card
Because of Apple’s policies regarding in-app purchases, Spotify doesn’t allow you to subscribe directly through the app. But don't worry—getting Premium on your iPhone is still quick and easy. Here is exactly how to do it. Why Can’t I Buy It in the App?
: If you subscribed years ago via iTunes, you may need to cancel that legacy subscription in your iPhone’s Settings > Apple ID > Subscriptions and wait for it to expire before re-subscribing via the Spotify website.
: Head to Spotify.com on your mobile browser.
Spotify and Apple have a long-standing disagreement over the "Apple Tax"—the 30% commission Apple takes on all in-app subscriptions. To avoid passing that cost onto you or losing profit, Spotify disabled the option to sign up within the iOS app. Step-by-Step: How to Subscribe to Spotify Premium