$1B is a high bar, but there are probably examples. Another comment mentions MCAS, but maybe that's too easily classified as a management failure. Out of curiosity I looked up a couple of other contenders, but neither made the cut.

However, that search took me to an example that I didn't recall, resulting in loss of life. I'll probably reference this story about the Therac-25 in the future as it hits on a number of clear software engineering failures:

-- https://www.bugsnag.com/blog/bug-day-race-condition-therac-2...