Assistance needed writing an NMAP NSE script to detect open port on host and send a command

Question

I have a very specific problem that needs addressing regarding writing an NSE script for Nmap. Basically here is what I want the script to do:

1. Connect to a host and check for a supplied open port: E.G. 18000.
2. If the port is open: Connect to the host via the open port and send the following command to the host: "hello\n". Note: the "\n" is important in the command.
3. If the output of the sent command begins with the string "SeedLink", the response should be printed out, if not the response should be silenced.

Here is what I have tried so far:

-- HEAD --

description = [[
This is a simple script example that determines if a port has a seedlink server running.
]]

author = "Me"

-- RULE --

portrule = function(host, port)
        return port.protocol == "tcp"
                 and port.state == "open"
 end

-- ACTION --

action = function(host, port)
        local sock = nmap.new_socket()
        local status, err = sock:connect(host, port)
        if not status then
                return "Failed to connect"
        end

        local data = "hello\n"
        status, err = sock:send(data)
        if not status then
                return "Failed to send data"
        end

        local response = sock:receive()
        if string.sub(response, 1, 8) == "SeedLink" then
                return "Seedlink server is running"
        else
                return "SeedLink server is not running."
        end
end

I use the following command to run the script:

nmap --script=seedlink.nse localhost -p 18000

The expected output would bee:

SeedLink v3.3 (2022.096) EQM

This script works, but it tells me that there is no Seedlink server running, although I can verify that there is one by running:

telnet localhost:18000