Never mind, I read it as not having a physical subeta currency as well.

Nevertheless, if these are going to be physically shipped, then real cash only is fine. It's only if they'll be scanned and sent only as digital copies that there needs to be a subeta currency option.

I've copied and pasted the rules, as taken from the art market rules. If there's no physical copy, and they're not physically being shipped and only being given as a digital copy then yes, there needs to a subeta equivalent currency option. This can be in the form of csc, sp, subeta items. However, if the items are physical items and require being shipped then having a real cash only option is fine.