During the recession in 2009, American Airlines needed liquidity and Citibank (who issued their cobrand credit card) came in.

Part of the $2.9B package was Citibank buying $1B worth of air miles to give to their cardmembers.

https://dealbook.nytimes.com/2009/09/17/american-airlines-ge...

That created a liability on American's books, but because they controlled the redemption policy and capacity (and had an expiration date on miles once issued to customers) that they had some control on how the liability got called in.