You don't have the same mods installed on your computer as on the server: https://mclo.gs/DP622IB#L2514
The thing about that is that I've made sure to install the right versions before I added them through Aternos (I can provide screenshots if needed), up & down double checked and it still never works.
I have a few mods that are only clientside too but does that mean I have to remove those and keep only the ones installed to the server for it to work?
I'll try to do another double check and try again.