how do I register noip using GET method with NodeMCU

  HTTPClient client;

  if (client.begin(noipServer, 80)) {
    Serial.println("Connected to noip");

    client.println("GET /nic/update?hostname=seaurchin.ddns.net HTTP/1.0");
    client.println("Host: dynupdate.no-ip.com");
    client.println("Authorization: seaurchin@gmail.com:secretPwd");
    client.println("User-Agent: San NodeMCU Client/0.0 seaurchin@gmail.com");
    client.println();

    //Wait for response

    while (client.connected())
    {
      // stay in this loop until the server closes the connection

      while (client.available())
      {
        // The server will not close the connection until it has sent the last packet
        // and this buffer is empty

        char read_char = client.read();
        Serial.write(read_char);
      }
    }
    // close your end after the server closes its end
    client.stop();

the above code is not working, I want to be able to notify no-ip server for ip address the NodeMCU client is running on

I want to be able to notify no-ip server for ip address the NodeMCU client is running on

Where do you tell the noip server that?

Since I am using NodeMCU

I am using

#include <WiFiClient.h>

for the client object.

PaulS:
Where do you tell the noip server that?

by first calling

client.begin(noipServer, 80)

and then sending header message I mentioned in my opening post.

Your Authorization string is not correct. Encode seaurchin@gmail.com:secretPwd to Base64 using online tool. And use the encoded string as below:
client.println("Authorization: Basic c2VhdXJjaGluQGdtYWlsLmNvbTpzZWNyZXRQd2Q=");

Here your encoded string is c2VhdXJjaGluQGdtYWlsLmNvbTpzZWNyZXRQd2Q=.

Regards,
Mustafa