I am creating a map with one layer that has a transparency of 80 and publishing that to ArcGIS Server 10.8.1 and 10.9.1 as a dynamic service. I have tried this with both ArcMap 10.8 and ArcGIS Pro 2.9. This is being accessed from runtime 100.13 using a ArcGISMapImageLayer. The service loads fine using the runtime api but the layer that should have a transparency doesn't. In checking the opacity property for that layer it is still set at 1. So the transparency from the layer in the dynamic service doesn't seem to carry over to the opacity property in ArcGISMapImageLayer. Any ideas if this should be working or how to get it to work?
Perhaps the issue is the image format being requested. I recommend: