Address already in use.

Typically, only one usage of each socket address (protocol/IP address/port) is permitted.

This error occurs if an application attempts to bind a socket to an IP address/port that has already been used for an existing socket, or a socket that wasn’t closed properly, or one that is still in the process of closing.

For server applications that need to bind multiple sockets to the same port number, for example, the case where the client process is taskkilled and started again consider using setsockopt(SO_REUSEADDR).

Client applications usually need not call bind at all—connect chooses an unused port automatically. When bind is called with a wildcard address (involving ADDR_ANY), a WSAEADDRINUSE error could be delayed until the specific address is committed. This could happen with a call to another function later, including connect, listen, WSAConnect, or WSAJoinLeaf.

BOOL bOptVal = TRUE;
        int bOptLen = sizeof(BOOL);
        iResult = setsockopt(ListenSocket, SOL_SOCKET, SO_REUSEADDR, (char *)&bOptVal, bOptLen);
        if (iResult == SOCKET_ERROR)
        {
            char m[500];
            snprintf(m, 500, "%s %d: setsockopt failed, port %d failed with error: %d",
                __func__, __LINE__, port_number, WSAGetLastError());
            printf("%s\n", m);
            freeaddrinfo(result);
            closesocket(ListenSocket);
            WSACleanup();
            return -1;
        }

https://docs.microsoft.com/en-us/windows/desktop/api/winsock/nf-winsock-setsockopt