WiFi.config(ip, gateway, subnet);
I had the same problem and solved it by providing all 4 Parameters:
WiFi.config(ip, dns, gateway, subnet);
The missing parameters are not replaced by default-values, so if You use:
WiFi.config(ip, dns)
the gateway parameter is set to 0.0.0.0 and the packet is not sent.
Happy Holydays
hjw