Saw this in the console

(19:21:34) | Failed to call hook 'BuyCommand' on plugin 'TreePlanter v1.0.3' (FormatException: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.)
  at System.Text.StringBuilder.AppendFormatHelper (System.IFormatProvider provider, System.String format, System.ParamsArray args) [0x000ff] in <a8ed250850854b439cedc18931a314fe>:0 
  at System.String.FormatHelper (System.IFormatProvider provider, System.String format, System.ParamsArray args) [0x00023] in <a8ed250850854b439cedc18931a314fe>:0 
  at System.String.Format (System.String format, System.Object[] args) [0x00020] in <a8ed250850854b439cedc18931a314fe>:0 
  at Oxide.Plugins.TreePlanter.Lang (System.String key, System.String id, System.Object[] args) [0x0000e] in <b2a13bf4219649d2b258c9484824bdff>:0 
  at Oxide.Plugins.TreePlanter.PlantTree (BasePlayer player, UnityEngine.Vector3 spawnPos, System.String treeType, System.Int32 treeCost) [0x00066] in <b2a13bf4219649d2b258c9484824bdff>:0 
  at Oxide.Plugins.TreePlanter.BuyCommand (BasePlayer player, System.String cmd, System.String[] args) [0x00243] in <b2a13bf4219649d2b258c9484824bdff>:0 
  at Oxide.Plugins.TreePlanter.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x000e3] in <b2a13bf4219649d2b258c9484824bdff>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0​

Did you customize the messages at all?

I did. I take it you believe the issue is there. I'll review that thanks.

Turns out I had a variable in the wrong place. Once I removed it from the language file all was well. Marking solved.