HAProxy 503 Service Unavailable - POST with Headers

The backend is not forwarding traffic to the server and returns 503 service unavailable.
My server requires the exact URL and headers. If the header is not set, the server will return 401 unauthorized and if the URL is not set, the server will return 404 Not found.

My cfg file

global
    log         127.0.0.1 local0 debug
    chroot      /var/lib/haproxy
    pidfile     /var/run/haproxy.pid
    maxconn     1000
    user        haproxy
    group       haproxy
    daemon
    stats socket /var/lib/haproxy/stats

defaults
    mode                    http
    log                     global
    option                  httplog
    option                  dontlognull
    option http-server-close
    option forwardfor       except 127.0.0.0/8
    option                  redispatch
    retries                 3
    timeout http-request    10s
    timeout queue           1m
    timeout connect         10s
    timeout client          1m
    timeout server          1m
    timeout http-keep-alive 10s
    timeout check           10s
    maxconn                 3000

frontend  main 0.0.0.0:80
  option httpclose
  option forwardfor
  reqadd X-Forwarded-Proto:\ http
  http-request add-header X-Forwarded-Proto http

  default_backend             app

backend app
    balance     roundrobin
    server  app1 100.82.185.122:32401

I am testing as following

import csv
import requests
import time

#url='http://100.82.185.122:32401/services/collector/event' #DIRECT URL 
url='http://100.82.182.73/services/collector/event' #HA Proxy URL
authHeader = {'Authorization': 'Splunk {}'.format('f64e68e1-a6e4-46a1-8fe3-131023886841')}
reader = csv.DictReader(open('overheating_.csv'))
for row in reader: 
    #row['SystemUsage.AggregateUsage'] = 17
    #row['FanSensor.RPMReading'] = 3
    jsonDict = {"index":"dltk-test", "source":"csv", "sourcetype":"all-idrac", "event": row }
    #print (row)
    r = requests.post(url, headers=authHeader, json=jsonDict, verify=False)
    print (r.text)
    time.sleep(1)

Response

<html><body><h1>503 Service Unavailable</h1>
No server is available to handle this request.
</body></html>

HAProxy Logs

Jun 28 15:30:51 localhost haproxy[25389]: 100.82.183.41:41182 [28/Jun/2022:15:30:51.906] main app/app1 0/0/-1/-1/0 503 212 - - SC-- 0/0/0/0/3 0/0 "POST /services/collector/event HTTP/1.1"
Jun 28 15:30:52 localhost haproxy[25389]: 100.82.183.41:41184 [28/Jun/2022:15:30:52.913] main app/app1 0/0/-1/-1/0 503 212 - - SC-- 0/0/0/0/3 0/0 "POST /services/collector/event HTTP/1.1"

Please guide me what’s wrong here.

semanage port --add --type http_port_t --proto tcp 32401 to allow traffic on port 32401