How do I filter tasks that are not yet done?

Posted on behalf of Andrew Nixon. Original posting date 2013-12-10.

I am trying to use the api to get a list of all high priority items which are not yet done (priority being a custom field I have added) but it consistently returns all the high priority tasks.

My url (end part) looks like this :

/tasks?custom_field[Priority]=High&is_done is false

The filter on the customfield works so I only get items marked as high priority and I've tried other permutations and variations of the done flag bug nothing seems to work. The result set includes a done_on field which I've also tried filtering on to no effect.

Thanks