Status polling is a technique in which a client system asks a payment provider, at intervals, what has happened to a transaction. The client sends a read request quoting the payment's identifier, and the provider replies with the current payment status, such as pending, settled or failed. The client repeats the request until a final state is returned.
Polling is needed for an asynchronous payment, where the result is not known when the request is first accepted, as with bank transfers and many payouts. The alternative is a webhook notification, in which the provider informs the client when the status changes. Webhooks are more efficient, but they can be delayed or missed, so well-built integrations poll as a backup. Polling should be spaced out, with intervals that lengthen over time, to stay within the provider's rate limiting rules.