Can't Figure Out How To Pass Steam Web API A Int64

The Steam Web API has a function for getting information on a published Workshop file called GetPublishedFileDetails. It says I can make a request for multiple files, but I cannot figure out how to do this with Javascript. At the moment, I have to make multiple calls to the API, which seems unnecessary.

I've tried sending it an array, strings, everything I can think of.

        for (let index = 0; index < arrayOfAddonIds.length; index++) {
            $.ajax({
                type: 'POST',
                url: 'https://api.steampowered.com/ISteamRemoteStorage/GetPublishedFileDetails/v1/',
                data: {
                    'itemcount': 1,
                    'publishedfileids[0]': parseInt(arrayOfAddonIds[index]),
                },
                dataType: 'json',
            }).done((data) => {
                console.log()
                populateAddonList(addon_data);
            }).fail((err) => {
                console.log(err);
            }).always((data) => {
                var addon = data.response.publishedfiledetails["0"];
                if (addon.result == 1) {
                    for (let i = 0; i < Object.keys(data).length; i++) {
                        var addonObject = {
                            "title": addon.title,
                            "id": addon.publishedfileid
                        }
                        addon_data.push(addonObject);
                    }
                }
            });
        }

Is there a way I could achieve this in one call to the API?

This is also Electron app, maybe that opens up some possibilities.

I guess that you have to do an array like this:

data: {
    'itemcount': 3, // Increase itemcount
    'publishedfileids[0]': ID0,
    'publishedfileids[1]': ID1,
    'publishedfileids[2]': ID2, // Add items accordingly
},