First of all copy and search app id in portal to find this app
https://gis1.victorvilleca.gov/portal/apps/MapSeries/index.html?appid=81f47c04f52541ee8283cc63971e9541
Because it is nearmap_us layer can not load, that means, you must have a portal item named 'nearmap_us', so just search nearmap to find that portal item.
The problem is you do not have permission to access nearmap imagery. For example, this nearmap portal item owner no longer have permission.
The solution is here, click here see my another post
https://transparentgov.net/cleargov1/1469/how-to-use-nearmap-in-arcgis-online-and-arcgis-pro