A subscriber has unused data when the next payment is due. The purchase terms determine what happens to that balance.

## What does a top-up do?

A top-up purchases an eligible additional allowance for an existing service. The provider must support adding that package to the customer’s eSIM profile, the digital SIM used by their device. Coverage overlap alone is not enough to establish that it can be attached.

Present the top-up’s allowance, price, coverage, validity and activation behavior. Explain whether it starts immediately, follows another package or uses a different rule. An added package does not automatically extend the expiry of an older allowance.

## What does a renewal do?

A renewal starts another period of a continuing subscription. Before renewal, the app should show the subscriber the period, included service, expected charge and payment method. If renewal fails, the app should show payment recovery separately from service recovery. A successful payment retry does not by itself confirm that connectivity has resumed.

An upgrade or downgrade can take effect at a future period. Keep the requested change separate from the active plan until that date and outcome are confirmed.

## What should the purchase interface make clear?

Tell the customer what changes, when it changes and what they are approving. Retain the existing order identity if a response is uncertain. Encouraging another purchase can create an unwanted second charge.

After fulfillment, show the new package or period with its effective terms. Keep any usage observation time visible so a delayed network update is not mistaken for a failed purchase.

In your [usage and top-up flow](/products/esim/usage-and-top-ups), name the package the customer is buying. For [mobile plans](/products/esim/mobile-plans), show which billing period continues and when the next charge applies.

## Related resources

- [eSIM](/products/esim) (product)
- [eSIM connectivity guide](/docs/guides/esim/overview) (docs)
- [What is an eSIM?](/explained/esim/what-is-an-esim) (answer)

[Get an implementation brief](/learn/workspace?topic=esim)