The steps :
1. Create Idempotency-Key and saved in POS DB
2. Created refund for $10 for payment 3333
3. App crashed , need to find out if the refund was created
4. Invoked REST API and found out there are two existing refunds for $10 for this payment
5. Need to find out Idempotency-Key associated with each of them to determine which one is the one just created and if it was created at all