2 services across different clusters not able to communicate but can communicate on same cluster

I have 2 clusters of ec2 launch type and both ec2 instances have same security group nginx and test in same namespace (nginx_main) nginx cluster has only one service called nginx the task definition for nginx has one container with following specification network mode bridge port mappings 80 -> 80, 443 -> 443 service connect is on and service type is client only

test cluster has one service called black_ink_website_backend the task definition for black_ink_website_backend has one container with following specification network mode bridge port mappings 1339->1337 service connect is on and service type is client server

nginx serivce is the internet facing service and I am getting 504 upstream timeout error in nginx but if I start the service in same cluster I am not getting 504 and system is working

I would also like to point out that I am not using ALB, it is a single ec2 instance per cluster

1339 port is available in inbound rules

upstream blackInkWebsiteBackend {
    server black_ink_website_backend-3000-tcp.nginx_main:1339; # <-- service connect endpoint
}

server {
    client_max_body_size 2048M;
    listen 80;
    listen [::]:80;
    server_name : api.blackink.in;

    location / {
        proxy_pass http://blackInkWebsiteBackend;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $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;
    }
}

server {
    client_max_body_size 7M;
    listen 443 ssl;
    listen [::]:443 ssl;
    server_name api.blackink.in;

    ssl_certificate /etc/letsencrypt/live/api.blackink.in/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/api.blackink.in/privkey.pem;
    # Other SSL settings can be added here
    location / {
        proxy_pass http://blackInkWebsiteBackend;
        # Other proxy settings can be added here
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $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;
    }
}

here is my nginx config, and both services are running properly which I have verified in logs

also there is one more thing that if I run both of them on same cluster it works properly