My exported mod is not working.

Hello, I recently finished my first MCreator mod for Minecraft. Me and my friend were really excited to prepare it for our server and everything, but when we tested the mod in singleplayer, none of the items appeared. The mod was installed, but none of the elements appeared. I already looked at other reports of this bug and nothing seemed to help. The mod is also letting no one join my friend join his server. Were using the correct modloader and version, so what is going on? Thank you.