PLEASE HELP Necrozma Lunala Background Fusion won’t work

Hey Trainers.

Im suffering some kind of weird bug or something.
When I try to fuse Lunala and Necrozma
BOTH with Special Background, Lunala's Name doesn't turn blue in the fusion screen, what's the indication for 2 Background's will get fused together.
I would risk one fusion but only have energy for 1 more left.