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.
1. Log into your Substack account on your web browser and head to your Account Settings.
2. Under Subscriptions, click on the publication you want to update.
3. Click on "Upgrade to paid subscription".
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.