Hi Sam,
Please refer this post: ArcGISRestLayer URI Returning 404 Error
It looks the server you chosen is not an image service, it only support 4 types operation:
https://services.arcgis.com/JJzESW51TqeY9uat/ArcGIS/rest/services/DalbyFields/FeatureServer/0
Supported Operations: Query, Query Top Features, Generate Renderer, Validate SQL
And the valid service for example: http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StateCityHighway_USA/MapServer
Supported Operations: Export Map
Wish that’s helpful.
Regards,
Ethan