show pop-ups wtih raster values in an image service from a mosaic

[AurelieShapiro]

I have created a thematic mosaic dataset from many rasters, the advantage of the image service is that you can change symbology and have pop-ups on a raster.

I have calculated statistcs, analyzed the mosaic dataset and added a raster function and color map to show a thematic legend as unique values- so each category of my single band rasters have a color.

I would like to show this raster value in a pop-up in AGOL. This pop-up works in arcGIS Pro, no problem,

but in arcGIS online it says no information available. When I try and open the attribute table in AGOL I get the error "accessing data failed"

I have seen many image services with pop-ups, how do they work?

My image service:

Forests/Treecover_Loss (ImageServer)