Arduino Uno - http post request

Trying to send a http post request to a Home Assistant webhook. unable to get this going....

void sendShedOFF() {

if (client.connect(serverName, 8123)) {
client.println("POST /api/webhook/shed_door_open HTTP/1.1");
client.println("Host: 10.1.1.24");
client.println("Connection: close");
client.println("Content-Type: application/json");
client.println("Content-Length: ");
client.println();
}
client.stop();

}

Appreciate any pointers you might have. Cheers Markus

value for Content-length header and body of the request are missing