Hello Nahuel thank you for your reply. Unfortunately I already tried to add a size to all the images. Could there be any other information missing? The experiment works fine in builder.
Thank you very much!
I don’t think the size units matter for it to work (not sure if deg and cm are supported for online experiments though). You can see how different units work here. I think the default in exp settings (File->Preferences->General->Units) is norm, but often height or pix are more convenient.