A few specifics about Oceania’s ShipBoardCredit (SBC):
It comes in four varieties, three of which you’ll see on your Oceania invoice and one that you may find on your TA’s invoice.
On the O invoice (Amenities and Gifts section), you may see SBC noted as OCAPP (you can search here on CC for my, and others’, explanation of OCAPP), and, depending on O Club status, you may/should see O Club SBC and complimentary gratuities (plus other perks). You may also find SBC assigned by O as compensation (negotiated or otherwise) for a prior cruise issue and/or purchased outright as a gift (by you, a TA, et al.).
The fourth source (which should not appear in the O invoice) is your TA’s own $ contribution (perhaps as a share of its commission) to your cruise enjoyment. It should be specified on your TA’s invoice as well as on a “gift card” you’ll find in your cabin on embarkation day. Note that this does not include any TA rebate $$$.
Most importantly, there is a difference in SBC. Any complimentary SBC that appears on your Oceania invoice is non-refundable. Any SBC you find on your TA’s invoice (that is not OCAPP with the TA’s (or it’s consortium’s) name next to it, should be refundable.
One truly good thing about O’s accounting is that, when shipboard purchases are made, non-refundable $$$ will always be tapped first. However, it is important to note that, should you make purchases pre-cruise (e.g., excursions, cooking classes, LaReserve) your bank of Oceania provided SBC will automatically be charged unless you indicate that you want to pay for the item with your credit card.
As for what SBC can purchase once onboard, non-complimentary (O Club) gratuities are included as are bar and various service charges. The main exception excluding use of SBC is deposits on future cruises (or purchase of a Future Cruise Certificate. Since we are not casino users, I cannot comment of that (though I doubt you could change non-refundable SBC into cash).
A final note: Always double check your ShipBoard account prior to disembarkation (there can be errors-particularly as regards bar charges). You can choose to have any unused refundable SBC given to you as cash on the final morning or, by default, returned to your credit card on file.