I investigated this a little bit.
My scenario is:
1. I have an AJAX call for a webserver that is in the same server as the CWP instance
2. This webserver communicate with CWP API for account creation. In other words, I have a PHP script in a CWP account that will use CWP API of its own server to create other accounts.
When the account is created directly with the CWP API, it returns 503 error (I isolated this using postman to communicate directly with CWP API), this is what is the described error in this post.
But, what I noticed is that when I create the account running the AJAX request, this request also returns 503 error. So, it looks like when an account is created using CWP API, the whole server became inaccesible by a small time, and not only the API webserver. This is a major issue for me.