In 2015, my team updated the credit card number check in the Uber rider app and it accidentally started blocking Chinese cards — our fastest growing country.
This was, of course, just before the Christmas store shutdown 
https://twitter.com/RebeccaSlatkin/status/1198821836315869184 …
If a card number starts with 34 or 37, it’s an Amex card and 15 digits long. If it starts with a 51-55, it’s a Mastercard and 16 digits long. Etc.
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If it starts with a 62, it’s a China UnionPay card and 16 to 19 digits long. We advanced at 16 digits, so most users could never type their full card number.
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