The same thing, apparently the developer simply forgot to add the folder with images for battles, so it is impossible to complete any battle in the game.
At first, I wanted to replace all the missing files with my random images, but after ~10 pictures I got tired, because you need to create an image with the name specified in the error, click "Retry" and create the next image.
I've decided to postpone the game until the next update
I think the developer will fix it soon