Hi @wint0178, when you logged in to the server, if you see this error, it was happened before login.
If it comes only one time and all other functions are working as expected, please ignore this error.
@skywatch I was able to setup several MQTT Gateways using NodeMCU boards with attached I2C sensors. The Gateways are all Wifi gateways, but I have been able to use my DDNS in place of the IP address to send data from several locations including one that is international. I think this is working well at this point. Thank you for your reply!