Chime, an online banking startup with about five million customers, has been suffering an outage over the last day that has made it impossible for those customers to get hold of their money.

According to this article from Bloomberg, the outage initially disabled the bank’s debit cards, too, leaving customers stranded. The debit cards were working again, the article says, but the company’s website and app were still mostly down. The reaction on Twitter has been predictably bad.

Chime has been growing quickly, and is currently in discussions about raising another round of financing at a valuation of $5 billion or more, the article says, adding that the outage doesn’t appear to have affected the fund raising.

Not many customers have a lot of good things to say about their traditional bank, and online banking and financial services are here to stay. However, there is one thing traditional banks generally do well, and that’s give customers their money when they want it. 

Online banking startups would do well to keep that in mind as they expand. After all, it seems fair to wonder if free, interest-bearing checking accounts and 24-hour, mobile access will be worth much if customers don’t believe Chime and its peers are reliable custodians of their hard-earned cash.