I am using Zap hosting not LAN or anything like that.

This is the error that starts upon anouther player joining. There is no error on serverside so im assuming its client side
[08:04:56] [Render thread/ERROR]: Error executing task on Client
java.lang.IllegalStateException: Invalid packet received, aborting connection
    at net.minecraftforge.network.NetworkHooks.validatePacketDirection(NetworkHooks.java:92) ~[forge-1.18.2-40.2.0-universal.jar%23127!/:?]
    at net.minecraftforge.network.simple.IndexedMessageCodec.consume(IndexedMessageCodec.java:152) ~[forge-1.18.2-40.2.0-universal.jar%23127!/:?]
    at net.minecraftforge.network.simple.SimpleChannel.networkEventListener(SimpleChannel.java:72) ~[forge-1.18.2-40.2.0-universal.jar%23127!/:?]
    at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247) ~[eventbus-5.0.3.jar%232!/:?]
    at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239) ~[eventbus-5.0.3.jar%232!/:?]
    at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302) ~[eventbus-5.0.3.jar%232!/:?]
    at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-5.0.3.jar%232!/:?]
    at net.minecraftforge.network.NetworkInstance.dispatch(NetworkInstance.java:68) ~[forge-1.18.2-40.2.0-universal.jar%23127!/:?]
    at net.minecraftforge.network.NetworkHooks.lambda$onCustomPayload$1(NetworkHooks.java:78) ~[forge-1.18.2-40.2.0-universal.jar%23127!/:?]
    at java.util.Optional.map(Optional.java:260) ~[?:?]
    at net.minecraftforge.network.NetworkHooks.onCustomPayload(NetworkHooks.java:78) ~[forge-1.18.2-40.2.0-universal.jar%23127!/:?]
    at net.minecraft.client.multiplayer.ClientPacketListener.m_7413_(ClientPacketListener.java:1824) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.network.protocol.game.ClientboundCustomPayloadPacket.m_5797_(ClientboundCustomPayloadPacket.java:57) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.network.protocol.game.ClientboundCustomPayloadPacket.m_5797_(ClientboundCustomPayloadPacket.java:7) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.network.protocol.PacketUtils.m_131356_(PacketUtils.java:22) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.util.thread.BlockableEventLoop.m_6367_(BlockableEventLoop.java:157) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.util.thread.ReentrantBlockableEventLoop.m_6367_(ReentrantBlockableEventLoop.java:23) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.util.thread.BlockableEventLoop.m_7245_(BlockableEventLoop.java:131) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.util.thread.BlockableEventLoop.m_18699_(BlockableEventLoop.java:116) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.client.Minecraft.m_91383_(Minecraft.java:1015) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.client.Minecraft.m_91374_(Minecraft.java:665) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at net.minecraft.client.main.Main.main(Main.java:205) ~[client-1.18.2-20220404.173914-srg.jar%23122!/:?]
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[?:?]
    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
    at java.lang.reflect.Method.invoke(Method.java:568) ~[?:?]
    at net.minecraftforge.fml.loading.targets.CommonClientLaunchHandler.lambda$launchService$0(CommonClientLaunchHandler.java:31) ~[fmlloader-1.18.2-40.2.0.jar%2317!/:?]
    at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-9.1.3.jar%235!/:?]
    at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:53) [modlauncher-9.1.3.jar%235!/:?]
    at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:71) [modlauncher-9.1.3.jar%235!/:?]
    at cpw.mods.modlauncher.Launcher.run(Launcher.java:106) [modlauncher-9.1.3.jar%235!/:?]
    at cpw.mods.modlauncher.Launcher.main(Launcher.java:77) [modlauncher-9.1.3.jar%235!/:?]
    at cpw.mods.modlauncher.BootstrapLaunchConsumer.accept(BootstrapLaunchConsumer.java:26) [modlauncher-9.1.3.jar%235!/:?]
    at cpw.mods.modlauncher.BootstrapLaunchConsumer.accept(BootstrapLaunchConsumer.java:23) [modlauncher-9.1.3.jar%235!/:?]
    at cpw.mods.bootstraplauncher.BootstrapLauncher.main(BootstrapLauncher.java:149) [bootstraplauncher-1.0.0.jar:?]
[08:04:56] [Render thread/INFO]: JEI StartEventObserver received class net.minecraftforge.client.event.ClientPlayerNetworkEvent$LoggedOutEvent
[08:04:56] [Render thread/INFO]: JEI StartEventObserver transitioning state from JEI_STARTED to DISABLED
[08:04:56] [Render thread/INFO]: Stopping JEI
[08:04:56] [Render thread/INFO]: Removed all colony views
[08:09:22] [Render thread/INFO]: Stopping!
[08:09:22] [Render thread/INFO]: Shutting down map thread

JEI is causing it 

Could be an outdated version with the modpack or one that is to modern for the earlier Minecraft version

Make sure the compatibility mods/ mod library mods are installed!

Message me if you have any further questions