Custom auth get 400 error with CONFIGURATION_NOT_FOUND

[SLdragon]

Follow the document to run custom auth code, but get the errors as below, did I miss something to config?

{
   "code":"auth/internal-error",
   "message":{
      "error":{
         "code":400,
         "message":"CONFIGURATION_NOT_FOUND",
         "domain":"global",
         "reason":"invalid"
      }
   }
}