Custom tiles not showing in menu

EDIT: Found the solution. The file extension is case sensitive. So .png instead of .PNG.

Hi, I'm having trouble getting custom tiles to show up in the menu. I've got a bunch of custom tiles from here: https://steamcommunity.com/app/259680/discussions/1/610574106419962078/ The sprites are 128x128 PNG files, and I've placed them here: C:\Users(username)\T-Engine\4.0\tome\data\gfx\custom-tiles

I'm running the Steam version of the original game and haven't played yet, just in case the feature is an unlock or something. I've also tried saving them as 64x64 files, but to no avail. Also fwiw I'm using Windows 10.

I'd appreciate some help with getting this working, thanks!