Honeywell Error communicating with a Client port=503

[LJGutierrez]

I tried an application that uses a Modbus client using Port = 503. Reading and writing data using the Modbus master example and a couple of other Modbus master simulators from the WEB, the results were 100% correct. When I moved the application to the field to use it with a Modbus master module from the Honeywell DCS an error arose saying that the client is not available.
Questions to identify the problem: Shall the Nagel protocol be enabled in this case?; If the MB Client uses the UnitID as 255 (disabled), but if the Honeywell system sends a message using an ID 1 (for example), the Modbus client's response will use the same ID received from the master (an echo of the ID received) or the slave will change it? ... I am supposing here that the ID represents the Node Address.

[JensMertelmeyer]

Why don't you just record the traffic with Wireshark and find out?