To enable Stripe Checkout:

1. Create Payment Link (for $5 one‑time) and Checkout Links (for subscriptions) in your Stripe Dashboard.
2. Set the Success URL in Stripe to: https://YOURDOMAIN/upload.html?paid=1
3. Set the Cancel URL to: https://YOURDOMAIN/index.html#pricing
4. Paste each Stripe link into plans.json → the "url" field for the corresponding plan.

When Stripe redirects back to upload.html?paid=1, the upload form will unlock.