I don’t know why a black rectangle appears when the caustics are switched on
Can someone help me?
weird, it almost looks like there is a label on the bottle. It’s all the same material?
maybe increasing the number of light path bounces would help?
Yes, it’s all the same material
these are the render settings
even that didn’t help
Is the lighting from a sun light or environment map? For some reason the caustics don’t seem to work with infinite light sources passing through parallel (or nearly so) faces. As a workaround, you could try making the walls of the bottle taper in thickness.