TinkerDay 1, by day. Ben’s order, without an idempotency key.held €0.00 · charged €0.00 · Larkspur kept €0.00
Chapter 4 of 7
Pressed Pay twice
The shop’s payments ran smoothly until a slow morning. Ben pressed Pay, waited, and the till tried again. Ben wrote in, cross.
This chapter: When a payment request gets no answer, how do you retry without charging twice?
About this chapter
You will learn
- A timeout doesn’t mean it failed
- A retry can charge twice
- An idempotency key makes a retry safe
Words you’ll meet
- Timeout
- Giving up waiting for an answer: the request may still have worked.
- Idempotency key
- A unique name sent with a request, so a retry with the same name is done only once.
Step 1 of 4
Ben presses Pay. The till’s request gets no answer, a , so the till sends it again.
Predict how many times Ben is charged.