Failed loading report when using Power BI Embedded : error 403

I started by looking at the AppOwnsDataStarterKit. I have incorporated the AppOwnsWebApi in our own back-end. I have created there a end-point which which I could retrieve the datamodel of a service priccipal profile (Get EmbeddedViewModel) 

Our front-end is built using Angular. In this Angular application I am calling the endpoint "Get EmbeddedViewModel)" (which nicely gives back a list of reports and also an embedtoken. This info is used to fill in the EmbedReportConfiguration. I am only interested in the first report.

       this._powerBIServiceProxy.retrieveEmbeddedModel().subscribe(vm => {this.viewModel = vm

            var report = this.viewModel.reports[0];

            this.reportConfig = {

                type: 'report',

                id: report.id,

                embedUrl: report.embedUrl,

                accessToken: this.viewModel.embedToken,

                tokenType: models.TokenType.Embed,

                permissions: models.Permissions.Read,

                viewMode: models.ViewMode.View,

                settings: {

                  layoutType: models.LayoutType.Master,

                  background: models.BackgroundType.Transparent,

                  panes: {

                    filters: { visible: false },

                    pageNavigation: { visible: true, position: models.PageNavigationPosition.Left }

                  }

                }

            }

 

When executing this code, I am getting an error message like this

 

I was hoping to see some more info in the technicalDetails, but... bad luck:-)

 

Any ideas what I could be doing wrong?