Below REST APIv2 query can help to get the list of all or specific publisher’s details such as publisher ID.

https://<tenant-name>/api/v2/infrastructure/publishers?fields=publisher_id%2Cpublisher_name

​@venkatesanek , it looks like this will return all publishers and their corresponding publisher IDs. What if I only want the request to return a specific publisher’s publisher ID, what will the request look like? 

Yes, this REST APIv2 query will give the list of all publisher details. 

To query a specific publisher details, publisher_id field is needed. But there is no other query available to fetch the publisher_id of a specific publisher.

Thanks, ​@venkatesanek. We found our own way to query the specific publisher IDs.  Is there a way I can assign 2 or more publishers to a private app in an API request? Since publisher_ID field is required when creating a private app, in publisher_ID, I declare the values of publisher IDs in array but I encounter the error below: 

"Invalid publisher id, which must be an integer."

For visualization purposes, the publisher IDs are set like these: 

   "publisher_id": [
        "123",
        "456"
      ]

Shouldn't be many publishers inside publishers scope [] but single inside publisher scope {}? Like this:

"publishers": [
    {
      "publisher_id": "1",
      "publisher_name": "Publisher One"
    },
    {
      "publisher_id": "2",
      "publisher_name": "Publisher Two"
    }
]

 "publishers": [
    {
      "publisher_id": "string",
      "publisher_name": "string"
    }
  ],

Here is the schema to update an app with multiple publishers:

{
    "app_name": "test-app",
    "host": "app.example.com",
    "clientless_access": false,
    "private_app_protocol": "http",
    "protocols": [
        {
            "type": "tcp",
            "ports": [
                "80",
                "443"
            ]
        }
    ],
    "publishers": [
        {
            "publisher_id": "17"
        },
        {
            "publisher_id": "10"
        },
        {
            "publisher_id": "21"
        }
    ],
    "tags": [],
    "trust_self_signed_certs": "False",
    "id": "15"
}

​@notskope ​@ppp , thanks for the clarification! This worked!