The API is the same shape on all three: configure the environment once, mount an order, handle five events, tear down. Only the install and the platform setup differ.
The five events
onReady and onPaymentSubmitted are lifecycle moments, not statuses. Where a provider never reports readiness, the SDK synthesises onReady so your spinner still clears.
onPaymentSubmitted fires exactly once per order. Providers disagree on how the end of a payment arrives: some send their own “payment finished” message and never a status, some report a completed status and never a finished message, some send both, in an order that is not fixed. The SDK collapses that into a single callback, so you can act on it directly and do not need a guard of your own. A failure or a cancellation closes it, so a failed payment is never followed by a submission.
Status
onStatusChange is the one event that carries state. It delivers a status from a fixed set, whichever provider the order routed to:
Providers each have their own vocabulary —
paid, order_completed, succeeded all arrive as completed — and the SDK maps them before you see them, so you never write a per-provider status table. The raw code rides along as providerStatus for your logs.
onCancel and onError are derived from the same statuses. A failed status fires onStatusChange and onError; a cancelled status fires onStatusChange and onCancel. Handle a terminal state in one place or the other, not both, or you will run it twice. onError also fires for a failure that never reached the provider, such as its surface failing to load, which is the recoverable case.
completed has no dedicated handler — it arrives through onStatusChange only.
It is also not the signal to act on. Drive your flow from onPaymentSubmitted, which fires once whether or not the provider reports a status, and read completed as the provider’s own view of its order.
None of this is settlement.
completed is the provider’s view of its own order; the money moving is Meld’s TRANSACTION_CRYPTO_COMPLETE webhook to your backend. Credit users there and nowhere else.