def purchase_provisioned_capacity(accountId=None):
    """
    This operation purchases a provisioned capacity unit for an AWS account.
    See also: AWS API Documentation
    
    Examples
    The example purchases provisioned capacity unit for an AWS account.
    Expected Output:
    
    :example: response = client.purchase_provisioned_capacity(
    
    )
    
    
    :type accountId: string
    :param accountId: The AWS account ID of the account that owns the vault. You can either specify an AWS account ID or optionally a single '-' (hyphen), in which case Amazon Glacier uses the AWS account ID associated with the credentials used to sign the request. If you use an account ID, don't include any hyphens ('-') in the ID.
            Note: this parameter is set to '-' bydefault if no value is not specified.
            

    :rtype: dict
    :return: {
        'capacityId': 'string'
    }
    
    
    """
    pass
