Gateway does not receive message from Network server using UDP

I’m building my network server.
I’m implementing UDP and encountered a problem with sending messages back to gateway which is RAK7249. On network server I’m using IP and PORT from received UPD message header to determine gateway IP address/port and sending to this address PUSH_ACK, PULL_ACK, PULL_RESP but nothing is received on the gateway.
I’m pretty sure that I’m following all packet rules described here packet_forwarder/PROTOCOL.TXT at master · Lora-net/packet_forwarder · GitHub
I know that UDP ports are keep changing but is there a way to send a test UDP message to gateway and see it on the gateway logs?

I have same problem: I see correct PUSH_DATA and PULL_DATA datagrams from gateway but I have no success in sending ACKs and PULL_RESPs.
Gateway log shows nothing when I send data to it.
Any advice ?