Existing but not reachable now. Unavailable is not absent, and confusing the two is a common error.
Old English un- (not) prefixed to available, formed on avail, from Old French valoir (to be worth, to avail), from Latin valere (to be strong, be worth), named a thing that exists but cannot presently be drawn on.
Existing but not reachable at present, a state easily and wrongly confused with not existing at all.