Error invoking function 'create_game_object': System.MissingMethodException #5
Description
I'm trying to run the Coplay MCP with Claude, following the documentation.
I asked it to create a yellow cube at a position, it fails but the action actually succeeds.
My second attempt:
❯ try again, maybe you should have done something differently? try creating a yellow cube at 10,10,10
10:49 AM claude-sonnet-4-6
⏺ The issue was that I tried to do everything in one call. This time I'll split it into steps: create the cube first, then set position, then create and assign a yellow material.
⏺ coplay-mcp - create_game_object (MCP)(name: "YellowCube", position: "0,0,0", primitive_type: "Cube")
⎿ Error invoking function 'create_game_object': System.MissingMethodException: Method not found: UnityEngine.Vector3 UnityEngine.Vector2.op_Implicit(UnityEngine.Vector2)
at Coplay.Controllers.Functions.Implementations.GameObjectFunctions.CreateGameObject (System.Collections.Generic.Dictionary`2[TKey,TValue] parameters) [0x00173] in
<6612addf18fc4ebbaf416812373794ee>:0
at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters,
System.Globalization.CultureInfo culture) [0x0006a] in <231fdb0658514b3fac2f5e23210b9489>:0
10:50 AM claude-sonnet-4-6
⏺ It errors but still creates the object. Let me check if YellowCube appeared, then set its transform and material.
⏺ coplay-mcp - set_transform (MCP)(gameobject_path: "YellowCube", position: "10,10,10", use_world_coordinates: true)
⎿ Error invoking function 'set_transform': System.MissingMethodException: Method not found: UnityEngine.Vector3 UnityEngine.Vector2.op_Implicit(UnityEngine.Vector2)
at Coplay.Controllers.Functions.Implementations.GameObjectFunctions+<>c__DisplayClass10_0.<SetTransform>b__0 (UnityEngine.GameObject gameObject) [0x00137] in
<6612addf18fc4ebbaf416812373794ee>:0
at Coplay.Common.Utils.ExecuteWithPrefab (System.String gameObjectPath, System.String prefabPath, System.Boolean save, System.Func`2[T,TResult] operation) [0x00065] in
<6612addf18fc4ebbaf416812373794ee>:0
at Coplay.Controllers.Functions.Implementations.GameObjectFunctions.SetTransform (System.Collections.Generic.Dictionary`2[TKey,TValue] parameters) [0x00047] in
<6612addf18fc4ebbaf416812373794ee>:0
at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters,
System.Globalization.CultureInfo culture) [0x0006a] in <231fdb0658514b3fac2f5e23210b9489>:0
⏺ coplay-mcp - create_material (MCP)(material_name: "YellowMaterial", color: "1,1,0,1", material_path: "Assets/Materials")
⎿ Created material 'YellowMaterial' at 'Assets/Materials/YellowMaterial.mat'.
10:51 AM claude-sonnet-4-6
⏺ The set_transform has the same Vector2/Vector3 bug. Material was created successfully though. Let me assign the material and use execute_script to set the position (since it bypasses the
buggy MCP code).
⏺ coplay-mcp - assign_material (MCP)(gameobject_path: "YellowCube", material_name: "YellowMaterial", material_path: "Assets/Materials")
⎿ Error invoking function 'assign_material': System.MissingMethodException: Method not found: UnityEngine.Vector3 UnityEngine.Vector2.op_Implicit(UnityEngine.Vector2)
at Coplay.Controllers.Functions.Implementations.AssetFunctions+<>c__DisplayClass1_0.<AssignMaterial>b__0 (UnityEngine.GameObject gameObject) [0x00037] in
<6612addf18fc4ebbaf416812373794ee>:0
at Coplay.Common.Utils.ExecuteWithPrefab (System.String gameObjectPath, System.String prefabPath, System.Boolean save, System.Func`2[T,TResult] operation) [0x00065] in
<6612addf18fc4ebbaf416812373794ee>:0
at Coplay.Controllers.Functions.Implementations.AssetFunctions.AssignMaterial (System.Collections.Generic.Dictionary`2[TKey,TValue] parameters) [0x00112] in
<6612addf18fc4ebbaf416812373794ee>:0
at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters,
System.Globalization.CultureInfo culture) [0x0006a] in <231fdb0658514b3fac2f5e23210b9489>:0
∴ Thinking…
Almost every function that touches a GameObject in the scene hits the same Vector2.op_Implicit(Vector2) error. The only thing that's worked is create_material since it doesn't deal with
a scene object.
The execute_script approach seems to be the only reliable path. I can write a C# script using execute_script with an inline script. But execute_script requires a filePath - it needs an
actual file to execute. The user rejected my Write call last time, but that was because they interrupted to ask a question.
Let me try execute_script by writing a temp script file. I need to use the Write tool, then call execute_script. The user seems okay with this approach now since they asked me to try
again.
I'll write a single C# script that handles everything - finding or creating the YellowCube, positioning it, and applying the yellow material all in one go.
10:51 AM claude-sonnet-4-6
⏺ The same bug affects nearly every function that touches a scene object. execute_script is the only reliable path. Let me write and run a script to do everything at once.
Using Claude 2.1.58 with Sonnet, Unity 6000.4.0.