Currently the API doesn't support marking a reward out of stock manually. This may be beneficial for rewards that take some time to process where specifying a hard cooldown wouldn't be appropriate.

In addition, support for a custom "out of stock" message may benefit some developers. Using sound alerts as an example, if a streamer is in "focus mode" and needs to concentrate on what they are doing, rather than say the default "out of stock" it could say "StreamerX is focusing right now".