Windows MSYS2 MINGW64: Examples fail with "MQTT_ERROR_SOCKET_ERROR" or "Failed to open socket: : No error"

[KlausMu]

Hi,
I am able to compile and run all the tests in WSL2.

With Windows and msys2 mingw64 examples also compile.
./tests works well

./bio_publisher <IP of broker> 1883 test
gives
MQTT_ERROR_SOCKET_ERROR

./simple_publisher <IP of broker> 1883 test
gives
Failed to open socket (getaddrinfo): Die Anwendung hat die Funktion WSAStartup nicht aufgerufen, oder bei dieser Funktion ist ein Fehler aufgetreten. Failed to open socket: : No error

In case of BIO, I could track it down to file mqtt_pal.c line 402
ssize_t tmp = send(fd, (char*)buf + sent, len - sent, flags);
send returns with -1

I don't understand exactly what send is doing, but my guess is that this is a call to some winsock binary.
Do you have any advice on what to do?

Thanks in advance

Edit: this also happens when using
./bio_publisher test.mosquitto.org 1883 test
Isn't this exactly what the test is doing? Why does only bio_publisher fail, but test succeeds?