I was asked this question in Amazon's SDE2 interview. There was no blackboard to draw the design diagram nor I has time to get the estimates of this system. Only think was the system should be scalable.

Use Case:

1. You can request a physical locker from the website after you order a product.
2. Once assigned, you will get an OTP to open that locker to collect your product.
3. If you want to return that product, you will have to do the same step 1 and 2.
4. The delivery/pickup person will also need have a knowledge of locker and OTP for that locker to put/pick the product from your locker.

I was asked to give the answers to the interviewers question only. I was also asked how will you design a OTP system and GET or POST APIs. I am a bit unclear of this system. How to solve this problem?