PC Demon heart in journey mode

[McDAB]

Im playing a journey mode map, even when i set the difficulty to master, it still wont let me use a demon heart to get the extra slot, ive played normal worlds before back in 1.3 and could still use a demon heart on a character in expert then take it back to a normal world. I take it because the world and character are both journey then thisll mean i can't use one