proxy_pass https NGinx to Gloo - 502 SSL Handshaking

Question

I try to proxy requests with nginx to a GlooEdge API Gateway, but it keeps failing with a 502 error code and a message:

peer closed connection in SSL handshake while SSL handshaking to upstream, client: 172.24.0.1, server: myapp.mydomain.fr, request: "GET /api/selfcare/refunds HTTP/2.0", upstream: "https://XX.XXX.XX.XXX:443/selfcare/refunds", host: "myapp.mydomain.fr:20889"

Here is my nginx config:

upstream my_api {
    server myapi.mydomain.fr:443;
}

server {
    listen 80;
    return 301 https://$host:20443$request_uri;
}

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name myapp.mydomain.fr;

    ssl_certificate /etc/ssl/certs/nginx/myapp.mydomain.fr.pem;
    ssl_certificate_key /etc/ssl/certs/nginx/myapp.mydomain.fr.key;

    location /api/ {
        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-Host $host;
        proxy_set_header        X-Forwarded-Server $host;

        proxy_pass https://my_api/;
    }

    location / {
        proxy_pass http://my_app;
    }
}

I think i tried everything, i digged every website and documentation, but i'm still unable to make this work ...

Does anyone have an idea ?