modded server connection issue

[evianaxoxo]

i made a modded forge server (specifically an ATM8 1.19.2 server) with the intention of playing it with my sister. i was able to start and run the server fine and i was able to join it on my own computer, but my sister wasn't able to join, there was an error that said

Connection Lost

Internal Exception: io.netty.handler.codec.EncoderException: java.io.UTFDataFormatException: malformed input around byte 164

i tried allowing java through mine and my sisters firewall, disabling it, etc., but nothing worked. please help me lol

edit: i think its important to mention that we were able to play on a vanilla server fine on aternos (where the server address was insertnamehere.aternos.me) but i had the same issue when i tried making a server on shockbyte and a vanilla server by downloading the server files off of the mc website (where the address was an ip address), so i am assuming the issue is either with the mods or the ip address 

Edited March 17, 2023 by evianaxoxo