That is what I did 
I got a EdgeRouterX that is able to do tcpdump and hooked it between the server and the client. I collected a sequence of 3 requests and responses - working okay, since all devices were restarted.
The first is directed to another Server in the same net, requests #2 and #3 are sent to the W5500 server.
Wireshark could read the pcap file and produced this output:
(The pcap file is not uploadable here)
I can see pairs of FIN packets being sent back and forth, with the exception of the last, which has only the one sent from the server.
The data parts are matching those I sent and received, so I can confirm these are the three requests I sent.
I am lacking knowledge of all the other info shown, though…
Any suggestions of what to capture else?