Troubleshooting

How-to

"I installed the pack but nothing changed." Installing only makes the icons available. Apply the pack in your launcher's icon-pack setting (see apply it in your launcher).
"There's no icon-pack setting on my phone." Your launcher probably doesn't support icon packs — stock Pixel and Samsung launchers don't. Install an icon-pack-aware launcher (Nova, Lawnchair, Smart Launcher, Niagara, or Zenith Launcher) and apply the pack there.
"Some apps are themed, others aren't." The unthemed apps have no mapping for the exact version on your phone. This is expected; assign an icon by hand to match (see assigning a single icon).
"Tapping the pack just flashes a message and closes." That is the whole app — it shows a one-line reminder to apply from your launcher and then exits. It has no screen of its own.
"My icons look cropped or sit on a coloured tile." Both come from your launcher's icon-shape / adaptive-icon setting, not the pack. Adjust the icon shape or background style in the launcher (see icon shapes, masking & backgrounds).
"An icon didn't update after I applied the pack." Some launchers cache icons; re-applying the pack, or restarting the launcher, forces a redraw.