Hi, this is my first time using a Minecraft server or trying to use mods, so this may be an issue of me not doing it correctly, but every time I try to join my server with the mod active, it gives me this message. I have my server running "Fabric 1.19.2 - (Fabric API + Lithium + Phosphor)".

Are you sure that the client and the server have the mods installed. Just placing the mods in the server's mods folder won't work, they need to be installed on the client too. Without the full game output it is hard to tell what the problem is.