I have what it's probably going to be a very silly question.
I have a free trial account in ArcGis Online. When trying to configure pop-ups, the options "configure pop-up" or "remove pop-up" don't appear on the respective menu.
My guess is that you've added a layer (service) that has sub-layers in it. You need to click the layer name to expand it and see the sub-layers. The configuration is on the sub-layers menu.
It's on the sublayer menu where I mean there are no options like "configure pop-up" or "remove pop-up" as you can see on the screenshot attached.[ATTACH=CONFIG]20084[/ATTACH]
That layer is what is called a "map notes" layer for adding simple notes on top of the map. There is no option to configure the popup because map notes layers only have a title and description, not any more attributes.