Invoice lifecycle

An invoice is the primary payment request object in Meum.

Invoice statuses

Status	Description
`pending`	Initial or transitional state
`awaiting_payment`	Checkout URL active; waiting for customer
`quoted`	Checkout quote active with deposit address
`paid`	Full payment received and validated
`underpaid`	Partial payment received
`expired`	Invoice expired before full payment
`failed`	Payment failed
`cancelled`	Invoice cancelled
`refunded`	Platform detected refund during status polling (platform-emitted)

The refunded invoice status is set by platform status polling, not by a merchant refund API. Merchant-initiated refunds are not yet available.

Field	Description
`amount`	Requested order amount
`expected_amount`	Amount expected after quote (may differ with FX)
`received_amount` / `paid_amount`	Actual amount received
`difference_amount`	Delta between expected and received
`output_asset`	Settlement token identifier
`checkout_url`	Hosted checkout URL
`expires_at`	Expiration timestamp
`tx_hash`	On-chain transaction hash when paid

Creating an invoice with the same store_id + external_order_id returns the existing invoice instead of creating a duplicate.

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