Thank you so much for the quick reply!
Actually, I found my own solution. The issue was due to another plugin I was using, the HUD MAKER ULTRA, which does something different with the images it creates. Your plugin works perfectly and as intended. I should've trouble-shooted some more before posting my comment. Apologies!
I did have another query though. Is it possible to change the font of the dice roll result number to something else? Many thanks!