The plant rooted and then produced the leaves that we see or did those leaves come with the branch when you took it?

It seems like it's primarily impacting one leaf. Consider removing it and observe to see what else happens. The branch tip looks green and healthy. For WIW that is not rust. It could also be an indicator of not enough sun and too much moisture. Wish I could offer more but there really isn't a clear answer just yet.

Those leaves grew after I transplanted it in the beginning of May. I cut off 4 leaves as they were really bad...spots and turning yellow...I will try more sun...I also sprayed with fungicide just in case. Hoping I got it in time to save the plant. thanks

Ok great. Best of luck with it.

Based on the picture I don't see any reason why the plant needs to be saved. It may not be a pretty leaf but at this point it doesn't look like anything close to terminal.