- 
Make sure to use the correct embedURL, you're using /reportEmbed when you should be using /dashboardEmbed.
 
eventually, your code should look something like this:
$(document).ready(function () {
        // Get models. models contains enums that can be used.
        var models = powerbi.models; // or window.powerbi.models
        var embedConfiguration = {
            type: 'dashboard',
            id: 'dashboardID',
            embedUrl: 'https://app.powerbi.com/dashboardEmbed',
            tokenType: models.TokenType.Aad,
            accessToken: 'TokenString'
        };
        var $dashboardContainer = $('#embedContainer');
        var dashboard = powerbi.embed($dashboardContainer.get(0), embedConfiguration);
    });
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