502 bad gateway error on Django Nginx Graphql gunicorn application

Question

My technology stack is,

Django
Graphql
nginx
gunicorn

Below is the function which is used to reset the password.

It is using GraphQLClient call where I am providing api endpoint to reset the password.

def password_reset(request, token):
    message = ''
    messageStatus = False
    if request.method =='POST':
        password1 = request.POST.get('password1','')
        password2 = request.POST.get('password2','')
        client = GraphQLClient('http://leagueoftennis.com/graphql/')
        query = """
           mutation PasswordReset($password1: String!, $password2:String!, $token:String!){
             passwordReset(newPassword1: $password1, newPassword2: $password2, token: $token) {
               errors
               success
             }
           }
        """        
        variables = {'token': token, 'password1':password1, 'password2':password2}
        result = client.execute(query, variables)
        result_json = json.loads(result)
        if result_json['data']['passwordReset']['success']:
           message = "Your password has been set."
           messageStatus = True
        elif result_json['data']['passwordReset']['errors']:
            if 'nonFieldErrors' in result_json['data']['passwordReset']['errors']:
                message = result_json['data']['passwordReset']['errors']['nonFieldErrors'][0]['message']
            elif 'newPassword2' in result_json['data']['passwordReset']['errors']:
                message = result_json['data']['passwordReset']['errors']['newPassword2'][0]['message']            
            else:
                message = "Something Went Wrong. Try Again!"
        else:
           message = "Link is expired!"
    context = {
       'messageStatus': messageStatus,
       'message': message,
       'token': token,
    }
    template = loader.get_template('account/password_reset.html')
    return HttpResponse(template.render(context, request))

Above method is called when user clicks on below link,

http://leagueoftennis.com/activate/eyJlbWFpbCI6ImthbHBlc2h0YXdkZUBvdXRsb29rLmNvbSIsImFjdGlvbiI6ImFjdGl2YXRpb24ifQ:1qMLtK:IUaG2ZYF1vdavJhuVzXAsYotR3agrfPqnJzTpmijRU0

But in return I am getting 502 bad gateway error.

Below is my nginx config,

upstream sports_league {
    server web:8000;
}

server {

    listen 80;

    location / {
        proxy_pass http://sports_league;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        proxy_redirect off;
    }

    location /static/ {
        alias /code/staticfiles/;
    }

}

This is what I am seeing in logs

68.203.0.28 - - [20/Jul/2023:05:20:41 +0000] "GET /activate/eyJlbWFpbCI6ImthbHBlc2h0YXdkZUBvdXRsb29rLmNvbSIsImFjdGlvbiI6ImFjdGl2YXRpb24ifQ:1qMLtK:IUaG2ZYF1vdavJhuVzXAsYotR3agrfPqnJzTpmijRU0 HTTP/1.1" 502 559 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36" "-"
2023/07/20 05:20:41 [error] 23#23: *2 upstream prematurely closed connection while reading response header from upstream, client: xx.xx.xx.xx, server: , request: "GET /activate/eyJlbWFpbCI6ImthbHBlc2h0YXdkZUBvdXRsb29rLmNvbSIsImFjdGlvbiI6ImFjdGl2YXRpb24ifQ:1qMLtK:IUaG2ZYF1vdavJhuVzXAsYotR3agrfPqnJzTpmijRU0 HTTP/1.1", upstream: "http://172.19.0.3:8000/activate/eyJlbWFpbCI6ImthbHBlc2h0YXdkZUBvdXRsb29rLmNvbSIsImFjdGlvbiI6ImFjdGl2YXRpb24ifQ:1qMLtK:IUaG2ZYF1vdavJhuVzXAsYotR3agrfPqnJzTpmijRU0", host: "leagueoftennis.com"

Please suggest what I am doing wrong and needs to be fixed.