Downlink failed with status 500

I'm trying to downlink from Tago to a device Strega. The manual of this device tells me that the data of how to send a downlink as follows: payload = 31 and Port = 1. The problem when running the Analysis is that I get the following error: Downlink failed with status 500: {"message":"Cannot read property 'status' of undefined"}. I would like to know what a possible solution might be.