You likely used a slightly different shade of pink. Ensure your RGB is exactly 255, 0, 255.
A 24x24 canvas offers exactly 576 pixels. To make your emblem look professional from a distance, follow these design rules: Use High Contrast emblem ragnarok 24x24 bmp
If you used a brush tool or saved it with compression, the edges of your design might have blended with the pink, creating off-shade pink pixels that won't register as transparent. You likely used a slightly different shade of pink
The Ultimate Guide to Creating Ragnarok Online Guild Emblems (24x24 BMP) emblem ragnarok 24x24 bmp
Use this color for any area you want to be transparent in-game.