API errors trying getcount members of a group

The API gives a fatal error of just disregards selecting a group. Because of that it is not possible to do a getcount of the members of a group. Tried this locally and on the 4.7 sandbox.

Using:
'group' => "Newsletter Subscribers"
It gives a fatal error:
"error_message":"A fatal error was triggered: Newsletter Subscribers is not of the type Int"

Using:
'group_id' => "Newsletter Subscribers"
It doesnt give the fatal error but disregards the filter anyway.

$result = civicrm_api3('Contact', 'get', array(
'group_id' => "Newsletter Subscribers",
'options' => array('limit' => 9999),
));

Result:
"is_error":0,
"version":3,
"count":211 (which is the total number of contacts in the database)