Receive UDP broadcast message using ESP32

I have a javascript web program the broadcasts the message 'HF-A11ASSISTHREAD' on a UDP4 socket. The socket has the IP 255.255.255.255 and it has the port 48899.
I want to receive the broadcasted message using my ESP32. Once I have reveived the message, I want to be able send one back.
Can anyone point me in the right direction? I have been trying things out for a few hours now and I haven't had any luck.

I'm taking a step back from that because I realised that actually my wifi access point isn't working.
I'm using the code from here: arduino-esp32/WiFiAccessPoint.ino at master · espressif/arduino-esp32 · GitHub but without all the stuff in the loop.
The only thing in the loop at the moment is:

WiFiClient client = server.available();
Serial.println(client);

While there is no client connected, it prints 0. However when I connect to it, it still prints 0. The only other message I get is:
"dhcps: send_offer>>udp_sendto result 0"
Whyi is it not detecting that there's anyone connected to the AP?