If you're already a paid subscriber to a publication, you can view a paid post on the Substack app.
If you're a free subscriber, you'll see a paywall notifying you that the post is visible for paying subscribers only.
How do I become a paid subscriber?
At this time, you can't change your subscription plan directly on the Substack app and upgrading can only be done on a web browser.
1. Head to your Substack account Settings page or https://substack.com/settings/subscriptions.
2. Click on the free subscription that you'd like to upgrade.
3. On your manage subscription page, select "Upgrade to paid".
4. Choose which subscription plan you'd like and enter your card details. You'll then have immediate access to any past paid posts and be able to read any future paid posts on the app.