Is it possible to reference/filter by project custom fields from a task-level API search request?

[ktanen-chl]

Since it doesn't seem to be possible to pull data directly from a report, I am trying to use the API to get all the tasks that fit certain conditions, and one of those conditions is that a custom field, called Date Booked, is not null. However, when I put "project:DE:Date Booked_Mod=notnull" into the URL, I get this error message:

{"error":{"message":"Invalid Parameter: Search Parameter value \"project:DE:Date Booked\"","title":null,"msgKey":"exception.attask","attributes":[""],"code":0}}

Is what I'm doing possible, and if so, what am I doing wrong? Either way, please let me know. 

Thank you. 

[RandyRoberts]

There isn't enough information here to do any kind of troubleshooting.

What is the API call you're trying to use? From your description, you're trying to pull tasks by filtering for a project field.

Why can't you pull the data from a standard report?

[skyehansen]

I think it might just be a syntax issue? Instead try 

&DE:project:YourFieldName_Mod=notnull

[ktanen-chl]

That didn't work for me either.

[skyehansen]

As Randy mentioned, you might get a bit further if you post the call. Are you getting the same/similar error message or has something else changed?

[ktanen-chl]

The URL looks like this, but I have deleted the API key for security reasons:

https://citlabels.my.workfront.com/attask/api/v16.0/task/search?apiKey=apiKey&method=GET&parentID_Mo...

I believe the problem is that project(DE:[any custom field]) cannot be reached from a task-level API call. That's what I'm trying to find out.