Arcade script from Pro doesn't work in AGOL

[JamesBurton1]

I've got this arcade script I use in ArcGIS Pro to symbolize my layer based on whether or not it has a value in the specified field. It doesn't work when I try to put this into a web map. What do I need to change so I can use this for AGOl symbology? I'm trying to avoid adding a field just for symbolization. 

var x = $feature.PLAT_NUM;
IIF(IsEmpty(x), "Pending","Active");

[DavidSolari]

Odd, this expression works in the Map Viewer for Enterprise 11.1 just fine. Does adding an explicit "return" keyword at the start of line 2 fix things?

[KenBuja]

That expression will work properly. Make sure that there is no expression or field in the "Choose attributes" section before saving your expression. Otherwise you'll get the "There was an error" message