The interest free loan is more like $1B dollars. This $181M is the breakage, the left over gift card balances that are unlikely to be redeemed and they are recognizing as revenue. e.g. The $2 left on a $20 gift card that someone doesn't bother redeeming.

They also get another $1B of deposits from people loading money onto their app to pay for drinks. Starbucks is basically sitting on the equivalent of a small banks deposits at any given time.