Google Admin SDK API - HttpError 412 "Domain user limit reached. Contact Support."

I want to perform a load test of a python script which creates users in the GoogleWorkspace. The purpose of the load test is to confirm that 100 users can be created successfully using "Google_add.py".However, I faced the following Error.

>googleapiclient.errors.HttpError: <HttpError 412 when requesting https://admin.googleapis.com/admin/directory/v1/users?alt=json returned "Domain user limit reached. Contact Support.">

the load test I did and the result

①To create 50users →OK

②To create 100users →only the first 10 users were successfully created, and the others raised the above HttpError.

My license

Google Workspace Business Starter
In my recognition, up to 300users can be created by this lisence.

Questions

①What is "Domain user limit"?

②How can I avoid this error?

I remember that I had this error before, reviewing the documentation from Google here, I found this information.

<h4>Note: It makes reference to an API for resellers, on our case since we do not have access to use the reseller API it's best to contact support.</h4>

> This error occurs when your customer has reached their maximum seat
> limit. To resolve this issue, Use the subscriptions.changeSeats method
> and depending on their subscription plan, use the following:
>
> For FLEXIBLE, increase the maximumNumberOfSeats parameter.
> For ANNUAL, increase the numberOfSeats parameter.

If the issue is actually the number of seats you can actually contact Google Workspace support, and they can increase the number for you. Is a very simple process, and that one worked for me with this error.

However, if you are 100% sure that you didn’t reach the Maximum number of seats, you might have reached a quota limit for the Directory API.

> You cannot create more than 10 users per domain per second using the Directory API.

You can solved that issue by implementing Exponential Backoff.

As an extra advice, be careful when testing the creation of users in Google Workspace. When I was getting that error I kept testing by deleting users and creating new ones and I reached a different error message A request for user account creation is disallowed as we've detected some potentially abusive behavior. Please contact Google support for help.

For that error it is best to contact support, explain that you are running some tests of creation of users, and if they can remove the ban for you.