Fails to get gRPC method information

I enabled server reflection as [the guide](https://github.com/grpc/grpc-go/blob/master/Documentation/server-reflection-tutorial.md#enable-server-reflection),

but on the gRPC web ui fails to get gRPC method information, so that I can't choose which method to test nor fill the request data.
my server is written in go(1.13.7 darwin/amd64), and I'm using Mac OS.

Is there anyone who has same problem?

```
» grpcui -plaintext localhost:8080 130 ↵ saemi.park@sayongja-mich-geulub
gRPC Web UI available at http://127.0.0.1:59999/ // there's no error message
```