I figured it out using a WordPress REST API plugin and now it works with the Postman.
But, I might have another issue with PHP version.
I sometimes got the following message.
You had an error communicating with that API. cURL error 28: Operation timed out after 15001 milliseconds with 0 bytes received
So, I checked the status in the WordPress Admin and I found this.
7.0.13 - We recommend using PHP version 7.2 or above for greater performance and security. How to update your PHP version
Should I upgrade the PHP to resolve the cURL error? if so, pleaes let me know how to upgrade PHP from Google Could Platform Bitnami stack.