How can I get available license via Google Workspace Admin SDK?

On Google Admin screen, I can get numbers of available licenses and used licenses shown below:

How can I get these numbers via API?

Note: I read this question and tried, but not worked well.

-- EDIT: 2021/07/15 --

My request:

https://developers.google.com/admin-sdk/reports/reference/rest/v1/customerUsageReports/get

date: (few days before now)
parameters: accounts:gsuite_unlimited_total_licenses (comes from Account Parameters)

Response from API:

{
  "kind": "admin#reports#usageReports",
  "etag": "\"occ7bTD-Q2yefKPIae3LMOtCT9xQVZYBzlAbHU5b86Q/gt9BLwRjoWowpJCRESV3vBMjYMc\""
}

Expectation: I want to get the data same as 2 available, 1132 assigned as the GUI shows.

To be honestly, I'm not satisfying even if I can get info via this API, because it seems not responding real-time data like GUI.

Solution

I think there are 2 ways this information can be obtain, but I can confirm for only one of them.

1. Using the Report API that you mentioned.

NOTE : The report is not live data, so you must run the API call with a "date" parameter set at least 2 days before the execution date
Given that, you would have to run this GET method with the proper date in the {date} param

GET https://admin.googleapis.com/admin/reports/v1/usage/dates/{date}

Then you would need to parse through the parameters to find the desired license you are looking for.
reference - https://developers.google.com/admin-sdk/reports/reference/rest/v1/customerUsageReports#UsageReports
Here is how it look like after parsing

[
    {
        "BoolValue":  null,
        "DatetimeValueRaw":  null,
        "DatetimeValue":  null,
        "IntValue":  12065,
        "MsgValue":  null,
        "Name":  "accounts:gsuite_enterprise_total_licenses",
        "StringValue":  null
    },
    {
        "BoolValue":  null,
        "DatetimeValueRaw":  null,
        "DatetimeValue":  null,
        "IntValue":  12030,
        "MsgValue":  null,
        "Name":  "accounts:gsuite_enterprise_used_licenses",
        "StringValue":  null
    }
]

Important : The repot will always date 2 day back, so you can get the total number of licenses gsuite_enterprise_total_licenses in my example, and then use the Enterprise License Manager API to retrieve all currently assigned licenses

reference https://developers.google.com/admin-sdk/licensing/reference/rest

2. Using the Reseller API

Retrieving the information from the reseller point of view you would need to use the subscriptions.get method, providing your customerId and subscriptionId , calling the following GET request:

GET https://reseller.googleapis.com/apps/reseller/v1/customers/{customerId}/subscriptions/{subscriptionId}

The response of that would be a subscriptions resource, that contains various information about the license and the Seats object , which if you expand looks like this :

{
  "numberOfSeats": integer,
  "maximumNumberOfSeats": integer,
  "licensedNumberOfSeats": integer,
  "kind": string
}

numberOfSeats should be the total amount of licenses and licensedNumberOfSeats should be the number of users having that license assigned to them.
NOTE : in order to use this API , the given tenant should have a "fully executed and signed reseller contract" - https://developers.google.com/admin-sdk/reseller/v1/how-tos/prerequisites
Reference - https://developers.google.com/admin-sdk/reseller/reference/rest/v1/subscriptions