hello! i have ubuntu 20, lgsm, oxide and this plugin
plugin with error

(17:20:26) | Failed to call hook 'OnUserGroupAdded' on plugin 'ChatPrefix v1.2.0' (InvalidOperationException: Sequence contains no elements)
  at System.Linq.Enumerable.First[TSource] (System.Collections.Generic.IEnumerable`1[T] source) [0x00010] in <351e49e2a5bf4fd6beabb458ce2255f3>:0 
  at Oxide.Plugins.ChatPrefix.OnUserGroupAdded (System.String id, System.String groupName) [0x0004f] in <bb99def7e5c845fe8cb5cc73d8091c2a>:0 
  at Oxide.Plugins.ChatPrefix.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00629] in <bb99def7e5c845fe8cb5cc73d8091c2a>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <31122a27a2414cd799150f8677cf39d4>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0​

Does it generally work apart from this error?

not work

any other errors?
can u add me on discord? we can look together into that problem
Gonzi#1337

FirstOrDefault instead of First :)
OnPlayerChat should return true instead of false

all non-bool hooks should return true as the standard. unfortunately fewer and fewer people follow this

Failed to call hook 'OnUserGroupAdded' on plugin 'ChatPrefix v1.2.0' (InvalidOperationException: Sequence contains no elements)
  at System.Linq.Enumerable.First[TSource] (System.Collections.Generic.IEnumerable`1[T] source) [0x00010] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
  at Oxide.Plugins.ChatPrefix.OnUserGroupAdded (System.String id, System.String groupName) [0x0004f] in <60c44fa521924f7e918f3a1d4bb56779>:0
  at Oxide.Plugins.ChatPrefix.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00629] in <60c44fa521924f7e918f3a1d4bb56779>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <31122a27a2414cd799150f8677cf39d4>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <0fbce81d88d64454b3e7abb24df7026b>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <0fbce81d88d64454b3e7abb24df7026b>:0

How can I get rid of this?

Fixed in the latest version. 

Thanks Wulf