unexpected error when i used listing sample code in project selling-partner-api-samples

[DavidYang88]

Describe the bug
I had follow the whole process with read me and sucess started the project,But when i try to save setting i received a error "
There was unexpected error happened while saving the settings. Please try again."

Use case and programming language
The bug is related to the following use case and programming language:

• Use case: Listing sample save setting
• Programming language: TypeScript / JavaScript

Relevant code section
The root-cause of the bug is related to the following sections of the code:
I found request url http://localhost:3000/api/settings return status code 500.

To reproduce
Steps to reproduce the behavior:

1. Open http://localhost:3000/
2. click setting icon
3. add config field and click save
4. See error

Expected behavior
Should be save success

Screenshots, logs, or other

Additional context
None