POST requests with cookie

I'm trying to send post requests with payload to automate an entry. The url is: https://gleam.io/wOAtd/air-jordan-iii-free-throw-line.

# payload={email and address}
headers = {"user-agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36"}
r1 = requests.get('https://gleam.io/wOAtd/air-jordan-iii-free-throw-line')
print("r1",r1.status_code)
r2 = requests.post('https://gleam.io/set-contestant', data = payload,cookies = r1.cookies,headers = headers)
print("r2",r2.status_code)

I'm getting 200 from r1 but 500 from r2. What else should I do? If you provide an answer please explain what you look for in network".