If you don't already have an existing item and don't use your 500 Coin for a new Stream, your Coin will be carried across to the next month.
Unused Coin accumulates in your wallet which can help you to access items with a higher Coin value.
Stream Coins are only valid within the Upstream app and can’t be exchanged for cash, used elsewhere, transferred to other users or refunded during or on termination of your subscription