I want to fill in a project picker field with Automation for Jira

[Marco Brundel]

How is it possible to fill a customfield project picker field with Automation for Jira.

On our Jira Cloud i've a customfield project picker field with customFieldId=11581.

I tried 

"customfield_11581" : { "value": "Projectname" }

and also

"customfield_11581" : { "id": "12211" }

[Marco Brundel]

For sure, you're in the right way, just need to make some adjustments into your code.
Follows below a code that I've built for you to this case:

{

    "update": {

        "Oplosgroep Jira Project": [

            {

                "set": {"id": "12211"}

            }

        ]

    }

}

The code above I've utilized the field name "Oplosgroep Jira Project", because will be easy to manage.
But you can use the custom field ID, as follow below:

{

    "update": {

        "customfield_11581": [

            {

                "set": {"id": "12211"}

            }

        ]

    }

}

Note: This id: 12211 need to be one of field value id.

[Aron Kuch]

That worked for me. Thank you!

[frother]

Hi Marco,

Thanks for getting in contact.

It appears that the Jira rest API for the project custom field is broken. The correct syntax is as you say:

"customfield_11581" : { "id": "12211" }

Although even hitting the rest API directly, the request is successful, but the field never updates. 

https://developer.atlassian.com/server/jira/platform/jira-rest-api-example-edit-issues-6291632/

Sorry,
Scott