I am hosting a server on Aternos, I run the TLauncher and have downloaded the SecurityCraft mod. I join the server and i can see all the new items exist but everytime I am trying to put any item it instantly disappears.

Install SecurityCraft on your server as well (put the mod file into the mods folder) and start the server with the forge-blablabla.jar file, not with the minecraft_server_blabla.jar file.
As we use this issue tracker for bug reports, and since this is not an issue with the mod, I will close this. If you need further assistance, feel free to join our Discord server.