I enabled a payment gateway but it doesn't show at checkout — why?

Only gateways that are enabled and set up appear at checkout. Check that:

1. The Online Payments plugin is active.
2. The gateway is enabled on Settings → Store Settings → Payment Gateway and is included in your plan.
3. Its credentials are saved for the mode you are using (test or live).
4. The gateway supports your store's currency. A gateway is hidden when the order currency is not one it accepts.

Also check the store is not still in Demo mode, where orders cannot be placed at all.