Symfony and nginx - 502 Bad Gateway error when calling APIs - php

Question

I use docker (php7.4 and nginx) for running my Symfony 5 application, I implemented Bearer authentication using firebase/php-jwt, and can get a token successfully, but when I try to call the APIs using the token in the header, I get 502 Bad Gateway (See the Error) from nginx.
I am sure that the problem comes from my nginx configs, because when I use Symfony Local Web Server, it works.
nginx configuration:
server {
listen 80;
server_name my.local;
root /home/my/public;
location / {
try_files $uri /index.php$is_args$args;
}
location ~ ^/index\.php(/|$) {
fastcgi_pass my-app:9000;
fastcgi_split_path_info ^(.+\.php)(/.*)$;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
fastcgi_param DOCUMENT_ROOT $realpath_root;
internal;
}
location ~ \.php$ {
return 404;
}
location ~ \.php$ {
return 404;
}
error_log /var/log/nginx/my_error.log;
access_log /var/log/nginx/my_access.log;
}

Answer 1

I increased the buffer size and solved the problem:
server {
server_name my.local;
root /home/my/public;;
location / {
try_files $uri $uri/ /index.php$is_args$args;
}
location ~ ^/index\.php(/|$) {
fastcgi_pass my-app:9000;
fastcgi_split_path_info ^(.+\.php)(/.*)$;
fastcgi_buffer_size 128k;
fastcgi_buffers 4 256k;
fastcgi_busy_buffers_size 256k;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
fastcgi_param DOCUMENT_ROOT $realpath_root;
internal;
}
error_log /var/log/nginx/my_error.log;
access_log /var/log/nginx/my_access.log;
}