The order resource in Everifin Paygate API tries to reflect merchant’s order (in most cases there is relationship: one order - one payment, but some merchants have concept of orders with posibility of multiple payments - customers can add items to the same order later when some items of the order were already paid).
The payment process starts with creating the payment order. There is one related payment resource created automatically with each new order (amount is equal as the amount of the whole order).
Order can be updated (e.g. amount adjusted Update Order endpoint) and the behavior result is based on the status of the related payment resource:
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