Is there a API to understand if the Custom Audience is populated or not?

Question

1. Let's Suppose I've 1500 Customers in a file. Once I upload Customer Data using Marketing API to create Custom Audiences, How do I know What is the count of Customers that are populated in META Audiences?

2. Secondly, How do I know if the Audience is Valid or not?

3. Lastly, How can I get the count of total audience that is accepted in a bucket of Custom Audience?

I've tried using approximate_count_lower_bound and approximate_count_upper_bound but it doesn't clearly gives a number, I've assumed it as a range. But I don't think it justifies my purpose.

I've tried using delivery_status, it gives a status code, But I want a count of exact accepted audiences.

https://graph.facebook.com/v19.0/<custom_audience_id>?fields=customer_file_source,description,name,rule,rule_aggregation,sharing_status,data_source,approximate_count_lower_bound,approximate_count_upper_bound,delivery_status

Following is the response:

{
    "customer_file_source": "USER_PROVIDED_ONLY",
    "description": "Update Audience name",
    "name": "Updated Custom Audience",
    "data_source": {
        "type": "UNKNOWN",
        "sub_type": "ANYTHING",
        "creation_params": "[]"
    },
    "approximate_count_lower_bound": 1000,
    "approximate_count_upper_bound": 1000,
    "delivery_status": {
        "code": 300,
        "description": "The audience is too small to be used in campaign creation."
    },
    "id": "<custom_audience_id>"
}