Json Unmarshal

[negativeOne1]

Hey,
I'm trying to unmarshal some JSON response back into Protobuf.
but I'm getting
json: cannot unmarshal string into Go value of type map[string]json.RawMessage
and it's caused by the ID field
from

s := []byte(`{"id":"5eaacacc6149d0f8d4b6a36d"}`)
var rsp pb.IDMsg
unmarshaler = jsonpb.Unmarshaler{AllowUnknownFields: false}
if err := unmarshaler.Unmarshal(bytes.NewBuffer(s), &rsp); err != nil {
	t.Fatal(err)
}

pb.proto:

message IDMsg {
  pmongo.ObjectId id = 1;
}

pb.go:

type IDMsg struct {
	Id                   *pmongo.ObjectId `protobuf:"bytes,1,opt,name=id,proto3" json:"id,omitempty"`
	XXX_NoUnkeyedLiteral struct{}         `json:"-" bson:"-"`
	XXX_unrecognized     []byte           `json:"-" bson:"-"`
	XXX_sizecache        int32            `json:"-" bson:"-"`
}