You have the wrong Forge version or you accidentally placed the mod in the wrong directory (e.g., inside a mods/1.12.2 folder when it should be directly in mods ). Solution: Move the JAR file directly into the root /mods folder. Ensure you are not running Vanilla Minecraft.
Downloading .jar files from unofficial sources carries significant risks. Because adult mods are often hosted on re-hosting sites (like 9Minecraft or similar "mirror" sites), they are frequent targets for: File Name- Fapcraft-Mod-v1.1-Forge-1.12.2.jar