I'm not sure how to proceed after the error occurred

The Prototype Pollution attack was successful, but I don't know how to proceed with the attack later. The attack I tried was a method of manipulating the user value with korea_pocas in /debug logic through a taint attack, but it failed due to an error during the JWT authentication process. Other than that, I tried various other things, but since I lacked skills, I attacked pollution

I think I should use portotype pollution to attack outputFunctionName, but I don't know where the input will be injected. I think pollution will occur in the merge function, so I tried this and that because I think I should put it in the filename in /raw/:filename, it didn't work.. I think Young misunderstood, but even a small hint

I tried changing the user to korea_pocas because merge polluted the JSON.parse function. However, it failed, and it is difficult to proceed later. I need help