Nginx not asking for client cert when POST method with payload

Question

I have configured nginx for ssl-client-authentication. It is working fine for GET and POST (with out payload). But when we use POST with body, client is not passing the certificate.

1. Either nginx is not asking for the cert
2. Or the client(javascript) itself is ignoring the cert i'm not sure

Nginx Configuration

upstream abc-abc.com {
    ip_hash;
    server 172.16.x.x:8987;
}


server {
        listen 443 ssl;
        client_max_body_size 100M;
        ssl_protocols       TLSv1 TLSv1.1 TLSv1.2;
        ssl_certificate ssl/bundle.crt;
        ssl_certificate_key ssl/abc.key;
        ssl_verify_client optional;
        ssl_client_certificate /certs/client_ca.cert;


        # Use Server preference
        ssl_prefer_server_ciphers on;
        ssl_session_cache shared:SSL:10m;
        ssl_dhparam /etc/ssl/certs/dhparam.pem;
        server_name "~^abc-(?:[A-Za-z0-9]{0,21}[A-Za-z0-9])?-?abc.com";
        proxy_buffering off;
        error_log /proc/self/fd/2;
        access_log /proc/self/fd/1;
        server_tokens off;
        location = /robots.txt {
                return 200 "User-agent: *\nDisallow: /\n";
        }
        location / {
                proxy_pass https://abc-abc.com;
                proxy_set_header Host $http_host;
                proxy_set_header X-Real-IP $remote_addr;
                proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
                proxy_set_header X-Forwarded-Proto $scheme;
                # HTTP 1.1 support
                proxy_http_version 1.1;
                proxy_set_header Connection "";
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection $connection_upgrade;
                proxy_read_timeout  36000s;

                proxy_set_header X-SSL-Serial $ssl_client_serial;
                proxy_set_header X-SSL-Verify $ssl_client_verify;
                proxy_set_header X-SSL-SDN $ssl_client_s_dn;
                proxy_set_header X-SSL-Cert $ssl_client_escaped_cert;
                proxy_set_header X-SSL-Fingerprint $ssl_client_fingerprint;
                proxy_set_header X-SSL-Start-Date $ssl_client_v_start;
                proxy_set_header X-SSL-End-Date $ssl_client_v_end;

        }
}

Please help, Thanks.