Stack Trace:
java.lang.IllegalArgumentException: Unable to find a field that matches {modifiers=[required: 10000, banned: 1000], type={ type input instanceof interface java.util.Map }}
at ProtocolLib.jar//com.comphenix.protocol.reflect.FuzzyReflection.getField(FuzzyReflection.java:352)
at ProtocolLib.jar//com.comphenix.protocol.injector.packet.PacketRegistry.createNewRegister(PacketRegistry.java:183)
at ProtocolLib.jar//com.comphenix.protocol.injector.packet.PacketRegistry.initialize(PacketRegistry.java:334)
at ProtocolLib.jar//com.comphenix.protocol.injector.packet.PacketRegistry.getClientPacketTypes(PacketRegistry.java:369)
at ProtocolLib.jar//com.comphenix.protocol.injector.PacketFilterManager.(PacketFilterManager.java:120)
at ProtocolLib.jar//com.comphenix.protocol.injector.PacketFilterBuilder.build(PacketFilterBuilder.java:121)
at ProtocolLib.jar//com.comphenix.protocol.ProtocolLib.onLoad(ProtocolLib.java:183)
at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:59)
at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:18)
at io.papermc.paper.plugin.storage.SimpleProviderStorage.enter(SimpleProviderStorage.java:39)
at io.papermc.paper.plugin.entrypoint.LaunchEntryPointHandler.enter(LaunchEntryPointHandler.java:40)
at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:549)
at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:324)
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1171)
at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:332)
at java.base/java.lang.Thread.run(Thread.java:1583)
Dump:
Parameters:
[NULL]
Sender:
com.comphenix.protocol.ProtocolLib@47a82fbb[
statistics=
packetTask=
tickCounter=0
configExpectedMod=-1
updater=com.comphenix.protocol.updater.SpigotUpdater@4001116d
redirectHandler=
scheduler=com.comphenix.protocol.scheduler.DefaultScheduler@46522b21
commandProtocol=
commandPacket=
commandFilter=
packetLogging=
skipDisable=false
isEnabled=false
loader=io.papermc.paper.plugin.manager.DummyBukkitPluginLoader@156895b6
server=CraftServer{serverName=Purpur,serverVersion=1.21-2246-ad910f8,minecraftVersion=1.21}
file=plugins/.paper-remapped/ProtocolLib.jar
description=org.bukkit.plugin.PluginDescriptionFile@4a1342f3
pluginMeta=org.bukkit.plugin.PluginDescriptionFile@4a1342f3
dataFolder=plugins/ProtocolLib
classLoader=PluginClassLoader{plugin=ProtocolLib v5.2.0-SNAPSHOT-679, pluginEnabled=false, url=plugins/.paper-remapped/ProtocolLib.jar}
naggable=true
newConfig=YamlConfiguration[path='', root='YamlConfiguration']
configFile=plugins/ProtocolLib/config.yml
logger=com.destroystokyo.paper.utils.PaperPluginLogger@4d76b72d
lifecycleEventManager=io.papermc.paper.plugin.lifecycle.event.PaperLifecycleEventManager@1676e133
allowsLifecycleRegistration=true
]
Version:
ProtocolLib v5.2.0-SNAPSHOT-679
Java Version:
21.0.3
Server:
1.21-2246-ad910f8 (MC: 1.21)

Thanks @Ingrim4 - I can confirm this fixed the issue.

[15:33:30] [Server thread/INFO]: This server is running CraftBukkit version 4226-Spigot-146439e-2889b3a (MC: 1.21) (Implementing API version 1.21-R0.1-SNAPSHOT)

Java 21

Yep works in the latest dev build. Thanks!

Should be fixed in the latest dev build so please use the latest dev build and try again: https://ci.dmulloy2.net/job/ProtocolLib/