ArcGIS Online is not Nearmap product, and as such any support you may need should be directed to Esri. Check out ArcGIS Online's support documentation at: https://www.esri.com/en-us/arcgis/products/arcgis-online/resources
NOTE: When Nearmap imagery is loaded in ArcGIS Online, the initial visibility range is set at 1:5,000,000. You might have to zoom in to be able to see the Nearmap imagery.