Calling Nginx from same system not working, getting 301 Moved permanently - docker

Question

I have Nginx server with domain name example.com and it servers
location / => for web, running docker at port 8080
location /api => for API, running docker at port 8090
There is another backend service running in docker at port 9000, which wants to call the API https://example.com/api ... If I try it as localhost:8090 then no issue.
But using https://example.com/api via Nginx returns 301 Moved permanent error.
That is, calling from the same system to Nginx is not working.
Not sure what is wrong.
Please find the nginx conf:
map $sent_http_content_type $expires {
default off;
text/html epoch;
text/css max;
application/javascript max;
~image/ max;
}
map $http_upgrade $connection_upgrade {
default upgrade;
'' close;
}
include /etc/nginx/conf.d/*.conf;
server {
listen [::]:443 ssl http2 ipv6only=on; # managed by Certbot
listen 443 ssl http2; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
index index.html index.htm index.nginx-debian.html;
server_name example.com;
location / {
proxy_pass http://localhost:8080/;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_set_header X-NginX-Proxy true;
}
location /api/v1/socketio/ {
proxy_pass http://lb_autosys_api/socket.io/;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
}
location /api/v1/ {
proxy_pass http://localhost:8090/;
}
gzip on;
gzip_types text/plain application/javascript application/x-javascript text/javascript text/xml text/css;
gzip_min_length 1000;
gunzip on;
gzip_vary on;
expires $expires;
}
server {
if ($host = example.com) {
return 301 https://$host$request_uri;
}
listen 80 default_server;
listen [::]:80 default_server;
server_name example.com;
return 301 https://$host$request_uri;
}