nginx proxy_pass not decoding automatically

Question

I am using NGINX as a proxy and my UI code is sending a payload

/?ddforward=https%3A%2F%2Frum.browser-intake-datadoghq.com%2Fapi%2Fv2%2Frum%3Fddsource%3Dbrowser%26ddtags%3Dsdk_version%253A4.24.1%252Cenv%253Astaging%252Cservice%253Acrestone-uat%252Cversion%253A4.1.3%252Cretry_count%253A183%252Cretry_after%253A500%26....

I have successfully been able to decode the URL but I am not able to decode the remaining URL (.com onwards) to go through the proxy.

This is the error that I am getting in my error.log when the request is sent:

[error] 1909930#1909930: *283 invalid port in upstream "https://rum.browser-intake-datadoghq.com%2Fapi%2Fv2%2Frum%3Fddsource%3Dbrowser%26ddtags%3Dsdk_version%253A4.24.1%252Cenv%253Astaging%252Cservice%253Acrestone-uat%252Cversion%253A4.1.3%252Cretry_count%253A183%252Cretry_after%253A500%26...

Here is my nginx config:

    server {
        listen       443 ssl http2;

        add_header Access-Control-Allow-Origin * always;
        add_header Allow 'GET, DELETE, HEAD, OPTIONS, POST' always;
        location / {
            error_log /var/log/nginx/error.log debug;
            resolver 8.8.8.8 ipv6=off;

            proxy_method 'POST';


     if ($args ~ "ddforward=(.*?com)") {
           set $ddforward $1;
    }
    if ( $ddforward ~ (.+)%3A%2F%2F(.+) ){ # fix :// between scheme and destination
             set $ddforward $1://$2;
   }
   if ($args ~ \.com(.*)$) {
        set $args_ddforward $1;
    }
 
            proxy_pass https://$ddforward$args_ddforward;

What can be done to decode the incoming $request_uri because it does not seem like nginx is doing this automatically. I apologize if my terminology is not correct, I am new to NGINX