Filebeat.netflow parse NAT log

Hello, I am using the netflow input of filebeat to parse data from NAT log. Fields in the NAT log are different from CISCO's netflow 9, so I use ''custom_definitions''. However, filebeat encountered an error with the message ‘netflow protocol version 772 not supported’.

I also use udp input to receive data. '\ufffd' appears in the received data and I suspect there is a problem with the data received in this way.