https://www.cnbc.com/2018/02/23/instacart-discovers-a-bug-that-withheld-tips-and-overcharged-users.html

Grocery delivery start-up Instacart has discovered a bug in its checkout flow that affected some of their users' ability to waive service fees and some shoppers' ability to receive tips.

In a blog post, the company says the bug was related to product updates made at the end of 2017 and fixed this week.