- [ ] Feature should be Heroku friendly.
- [ ] Prevent oneliner if-statement.
- [ ] Use early return for negative case as much as possible.
- [ ] Validate all external inputs (including data from partner API).
- [ ] Error or failure cases are handled.
- [ ] Provide actionable error message as much as possible.
- [ ] Unit test friendly interface and unit test included.

Hey reviewers, please check the followings if appropriate.

- [ ] Feature should be Heroku friendly.
- [ ] Prevent oneliner if-statement.
- [ ] Use early return for negative case as much as possible.
- [ ] Validate all external inputs (including data from partner API).
- [ ] Error or failure cases are handled.
- [ ] Provide actionable error message as much as possible.
- [ ] Unit test friendly interface and unit test included.

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