and this is the error message in the inspector:
note: the image of this element has been modified by an action, the data source property above is therefore not applied
Do you have an image element in the popup, or have you set the popup’s background to an image?
I suspect you may have misunderstood the Display data action. This only loads the data (in this case the URL of the image as text) to the popup, but it doesn’t actually show anything. Setting the popup’s data type to image just means it’s storing the image URL.
Apologies if I’m pointing out obvious things, but not knowing your skill level, that was my guess.
As for the warning, that’s really just FYI for the debugger. Since an action has modified the data source, the debugger may show the incorrect source. It’s not related to why your image isn’t showing.