Bad gateway error .Error 502

Help!
1

Hi im using HAProxy version 3.0.8-6036c31 on opnsense as a proxy for several servers. ACME server is configured also.
this is server config:

#
# Automatically generated configuration.
# Do not edit this file manually.
#

#
# NOTE: HAProxy is currently DISABLED
#
global
    uid                         80
    gid                         80
    chroot                      /var/haproxy
    daemon
    stats                       socket /var/run/haproxy.socket group proxy mode 775 level admin
    nbthread                    4
    hard-stop-after             60s
    no strict-limits
    maxconn                     800
    ocsp-update.mindelay 300
    ocsp-update.maxdelay 3600
    httpclient.resolvers.prefer   ipv4
    tune.ssl.default-dh-param   4096
    spread-checks               2
    tune.bufsize                16384
    tune.lua.maxmem             0
    log                         192.168.0.90 syslog
    lua-prepend-path            /tmp/haproxy/lua/?.lua

defaults
    log     global
    option redispatch -1
    maxconn 1200
    timeout client 30s
    timeout connect 30s
    timeout server 30s
    retries 3
    default-server init-addr libc,last
    default-server maxconn 8000

# autogenerated entries for ACLs


# autogenerated entries for config in backends/frontends

# autogenerated entries for stats




# Frontend: 0_SNI_frontend (Escucha en 0.0.0.0:80 , 0.0.0.0:443)
frontend 0_SNI_frontend
    bind 0.0.0.0:443 name 0.0.0.0:443 
    bind 0.0.0.0:80 name 0.0.0.0:80 
    mode tcp
    default_backend SSL_Backend

    # logging options

# Frontend: 1_HTTP_frontend (Escucha en 127.4.4.3:80)
frontend 1_HTTP_frontend
    bind 127.4.4.3:80 name 127.4.4.3:80 accept-proxy 
    mode http
    option http-keep-alive
    option forwardfor

    # logging options
    # ACL: NoSSL_condition
    acl acl_67dc7229f0ca87.12416952 ssl_fc

    # ACTION: HTTPtoHTTPS_rule
    http-request redirect scheme https code 301 if !acl_67dc7229f0ca87.12416952

# Frontend: 1_HTTPS_frontend (Escucha en 127.4.4.3:443)
frontend 1_HTTPS_frontend
    http-response set-header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload"
    bind 127.4.4.3:443 name 127.4.4.3:443 accept-proxy ssl curves secp384r1  no-sslv3 no-tlsv10 no-tlsv11 no-tls-tickets ciphers ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES256-GCM-SHA384  ciphersuites TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256 alpn h2,http/1.1 crt-list /tmp/haproxy/ssl/67dd4f48dc7790.48843150.certlist 
    mode http
    option http-keep-alive
    option forwardfor
    timeout client 15m

    # logging options
    option dontlognull
    option dontlog-normal
    option log-separate-errors
    option httplog

    # ACTION: PUBLIC_SUBDOMAINS_rule
    # NOTE: actions with no ACLs/conditions will always match
    use_backend %[req.hdr(host),lower,map_dom(/tmp/haproxy/mapfiles/67dc72bb167027.30626723.txt)] 

# Backend (DISABLED): acme_challenge_backend (Added by ACME Client plugin)

# Backend: SSL_Backend ()
backend SSL_Backend
    # health checking is DISABLED
    mode tcp
    balance source
    # stickiness
    stick-table type ip size 50k expire 30m  
    stick on src
    server SSL_Server 127.4.4.3 send-proxy-v2 check-send-proxy

# Backend: EEST1_backend (Backend de server eest1/moodle)
backend EEST1_backend
    # health checking is DISABLED
    mode http
    balance source
    # stickiness
    stick-table type ip size 50k expire 30m  
    stick on src
    http-reuse safe
    server EEST1 10.10.10.101:443 send-proxy-v2 check-send-proxy

Whole proccess was made with this https://blog.holtzweb.com/posts/opnsense-with-haproxy-and-lets-encrypt/
It seems partially working despite bad gateway error
these are some of the logs to syslog:

xxx.xxx.xxx.xxxx:43160 [26/Mar/2025:15:28:14.196] 1_HTTPS_frontend~ EEST1_backend/EEST1 0/0/0/-1/1 502 209 - - SH-- 8/3/0/0/0 0/0 \"GET https://eest.tecnica1vl.org/favicon.ico HTTP/2.0\"

xxx.xxx.xxx.xxx:43160 [26/Mar/2025:15:28:13.787] 1_HTTPS_frontend~ EEST1_backend/EEST1 0/0/0/-1/1 502 209 - - SH-- 6/2/0/0/0 0/0 \"GET https://eest.tecnica1vl.org/tecmood/ HTTP/2.0\"

internal server is working actually with letsencrypt client and port forwarding with opnsense. (disabled when HAproxy is active)
Thanks in advance!