NTRIP client RTK message unknown to UBlox F9K

Question

I am requesting via NTRIP my correction values to a server. My server point is https://igs-ip.net/. After fetching and sending it over a broker which distributes it to my receivers. At the receiver side, I do send to and get at UART1 my bytes, but in the message view UBX->MON->MSGPP it only shows that all bytes are UNKOWN.

This is my code to fetch the correction data. I do get the correct response for my credentials.

    import base64
    import socket
    import time
    from pyrtcm import RTCMReader

    mqtt_client: MQTT = MQTT(cfg.ntrip.mqtt_config, "NTRIP_CLIENT")
    mqtt_client.open()

    dummyNMEA = "$GPGGA,143741.356,7839.493,S,07627.626,W,0,00,,,M,,M,,*45\r\n"

    username = cfg.ntrip.get("caster_user")
    password = cfg.ntrip.get("caster_password")
    port = cfg.ntrip.get("caster_port")

    pwd = base64.b64encode("{}:{}".format(username, password).encode("ascii"))
    pwd = pwd.decode("ascii")

    print("Header sending... \n")

    header = (
        f"GET /{cfg.ntrip.get('mountpoint')} HTTP/1.1\r\n"
        + f"Host {cfg.ntrip.get('caster_url')}\r\n"
        + "Ntrip-Version: Ntrip/2.0\r\n"
        + "User-Agent: NTRIP gopots/0.0\r\n"
        + "Connection: close\r\n"
        + "Authorization: Basic {}\r\n\r\n".format(pwd)
    )

    print(header)

    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((cfg.ntrip.get("caster_url"), int(port)))
    s.send(header.encode("ascii"))

    print("Waiting answer...\n")
    response = s.recv(1024).decode("ascii")
    print(response)

    while True:
        try:
            s.send(dummyNMEA.encode("ascii"))
            data = s.recv(1024)
            print(data)
            mqtt_client.send(data)
            time.sleep(1)
        except Exception as e:
            print(e)
            continue
    s.close()

At the other side, I just fetch the topic and pass through the data. By using the u-center build in NTRIP Client it works flawless.