Node message NACK received - why?

[mariusl]

Hi
I am new to mysensors. I don't think I understand enough to get going so any help will be appreciated.
I am running HA on a RPI3 with a Serial Gateway. I use the RFM95 radios on the Gateway and the node.
I can see the node message is received at the GW but I get a NACK back. I am not sure why or where to look for the issue.
Here is the message from the DEBUG output on the node

!TSF:MSG:SEND,0-0-1-1,s=255,c=3,t=8,pt=1,l=1,sg=0,ft=0,st=NACK:0

This is copied from the HA log file.
Some of the traffic

2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.transport] Receiving 0;255;3;0;0;0
2022-07-23 13:15:23 DEBUG (MainThread) [homeassistant.components.mysensors.gateway] Node update: node 0 child 255
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.transport] Receiving 0;255;3;0;9;1618933 TSF:MSG:READ,1-1-255,s=255,c=3,t=7,pt=0,l=0,sg=0:
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.handler] n:0 c:255 t:3 s:9 p:1618933 TSF:MSG:READ,1-1-255,s=255,c=3,t=7,pt=0,l=0,sg=0:
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.transport] Receiving 0;255;3;0;9;1618954 TSF:MSG:BC
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.handler] n:0 c:255 t:3 s:9 p:1618954 TSF:MSG:BC
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.transport] Receiving 0;255;3;0;9;1618962 TSF:MSG:FPAR REQ,ID=1
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.handler] n:0 c:255 t:3 s:9 p:1618962 TSF:MSG:FPAR REQ,ID=1
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.transport] Receiving 0;255;3;0;9;1618974 TSF:PNG:SEND,TO=0
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.handler] n:0 c:255 t:3 s:9 p:1618974 TSF:PNG:SEND,TO=0
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.transport] Receiving 0;255;3;0;9;1618984 TSF:CKU:OK
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.handler] n:0 c:255 t:3 s:9 p:1618984 TSF:CKU:OK
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.transport] Receiving 0;255;3;0;9;1618993 TSF:MSG:GWL OK
2022-07-23 13:15:23 DEBUG (MainThread) [mysensors.handler] n:0 c:255 t:3 s:9 p:1618993 TSF:MSG:GWL OK
2022-07-23 13:15:23 DEBUG (SyncWorker_7) [mysensors.persistence] Saving sensors to persistence file /config/mysensors/mysensors1.json