Order ID
Order ID is the number a panel returns when it accepts an order, and it is the only handle support can act on when something about that order goes wrong.
The add action returns little more than the ID. Everything afterwards refers back to it: a status request takes it, a refill request takes it, a cancel request takes it, and a support ticket without it usually gets a request for it before anything else happens. Store it the moment the panel returns it, including when you ordered through the website rather than through software.
Keep it with the rest of what you sent: the service ID, the link, the quantity and the time you placed it. The panel keeps its own record, but the value of yours is that it was written before anything could change. A service ID can be repointed at different supply, a service can be renamed or removed, and an order history read much later may no longer describe what you thought you were buying.
An order ID is local to the panel that issued it. When a reseller forwards your order upstream, the panel above issues its own number for the same delivery, and the two are unrelated. Your reseller stores the pair; you only ever see your own. Quoting your ID to the panel above yours means nothing there, which is part of why a dispute travels up a chain one step at a time instead of jumping to whoever delivered.