My friend can't join my server, help?

Me and my friend wanted to make a modded server using our own taste in mods. I added the mods like normal and downloaded the mods from curse forge using the correct versions. I was able to join the server totally fine with no problems, however the help comes in hand when my friend joins, i went through all the mods and we compared them to see if their the same and it is. Her forge is also the same and she has her mods in the correct folder. When she joins my server multiple messages are shown as following. When she presses connect is says "Failed to Connect : Internal Exception: java.io.IOException: An existing connection was forcibly closed by the remote host. I told her to try direct and it just says Disconnected, the server was online during this so I didn't seem to the know the problem. In the bottom right corner there was an ❌I asked her to hover her mouse over it to see if it shows any messages, as i thought it did, it said "Incompatible FML modded server: Server network message list is not compatible." I'm not great with technicians and I hope somebody can help me out to why this is being said. I've been trying to get her to connect for several hours now and I dont want to loose hope!