Need help on Nginx reverse Proxy

I have server whose URL is https://xx.xx.xx.xx/TestPage/ which gets generated as

https://xxxx.xxx.xxx/TestPage/(S(0inoxzi14rxqq1uix1tiyp1t))/index.aspx

Now I have implemented nginx reverse proxy in front of this server and then I have done the config proxy_pass as

proxy_pass https://xxx.ssss.sss.ss/TestPage;

Now if you see after TestPage there is a unique value gets added and then index.aspx however whenever request is passed through nginx I get 502 badgateway.

Wondering how do I pass that unique value through regex?

Please help

here is the location

location /TestPage {
client_max_body_size 10m;
client_body_buffer_size 128k;
proxy_send_timeout 90;
proxy_http_version 1.1;
proxy_read_timeout 90;
proxy_buffer_size 128k;
proxy_buffers 4 256k;
proxy_busy_buffers_size 256k;
proxy_temp_file_write_size 256k;
proxy_connect_timeout 30s;
proxy_pass https://xx.ss.xx.ss/TestPage;
proxy_redirect default;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;
add_header X-Content-Type-Options nosniff;
add_header X-XSS-Protection "1; mode=block";
add_header Referrer-Policy "no-referrer-when-downgrade";
}
}