Assigning users to GitHub Projectv2 Draft Issues

Question

I'm trying to update the assignee list for a GitHub ProjectV2 draft issue with my organization installation app using the updateProjectV2DraftIssue mutation but I keep getting as response of:

{
    "data": {
        "updateProjectV2DraftIssue": null
    },
    "errors": [
        {
            "type": "NOT_FOUND",
            "path": [
                "updateProjectV2DraftIssue"
            ],
            "locations": [
                {
                    "line": 1,
                    "column": 12
                }
            ],
            "message": "Could not resolve to DraftIssue node with the global id of '<ISSUE_ID>'."
        }
    ]
}

(where <ISSUE_ID> was the global node ID of the issue).

I also get the exact same issue when trying to add/remove assignees from an Assignable Issue/Pull Requests too when using the addAssigneesToAssignable mutation

I know that the node ID is correct as I'm using the value directly from a previous request that created the draft issue.

The mutation I am using is:

{
    "query":"mutation {
        updateProjectV2DraftIssue(
            input: {
                draftIssueId : \"<ISSUE_ID>\"
                assigneeIds : [
                    \"<USER_ID>\" 
                ] 
            } 
        ) {
            draftIssue {
                assignees(first: 100) {
                    nodes {
                        login  
                    } 
                }
            } 
        } 
    }" 
}

(where USER_ID is replaced with the User global node ID and ISSUE_ID with the issue global Node ID)

I'm unsure if this is an issue with my query or with the permissions of my Installation App. The current permissions it has are Repo: Metadata: read, Issues: read & write, Pull requests: read & write and Org: Projects: admin, Members: read