nginx regular expression reverse proxy location

I try to create a location based reverse proxy.
My config does not work as expected.

It should pass every request that is made to /api & /auth to the backend, and everything else to the frontend server.

server {

 listen 80;
 server_name 127.0.0.1 localhost;

 # remove server version
 server_tokens off;

 try_files $uri $uri/ =404;

 autoindex off;

 location = /favicon.ico { access_log off; log_not_found off; }
 location = /robots.txt  { access_log off; log_not_found off; }

 location ~ ^/(api|auth)/ {
     proxy_pass http://127.0.0.1:8080/$1;
     proxy_http_version 1.1;
     proxy_set_header X-Forwarded-Proto $scheme;
     proxy_set_header Connection $connection_upgrade;
     proxy_set_header Upgrade $http_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;
 }

 location ~ ^/(.*) {
     proxy_pass http://127.0.0.1:3000/$1;
     proxy_http_version 1.1;
     proxy_set_header X-Forwarded-Proto $scheme;
     proxy_set_header Connection $connection_upgrade;
     proxy_set_header Upgrade $http_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;
 }

}

The request to http://example.com/ seems to work correctly and it serves the frontend, but a request to /api or /auth returns a 404 error from the backend.

When i look on the reuqest URL that receives the backend, its always / and thats not correct.

What do i wrong?

EDIT: I got it working with the following changes:

    location ~ /(api|auth)/(.*)$ {
        proxy_pass http://127.0.0.1:8080/$1/$2;
        ...
    }

    location ~ /(.*)$ {
        proxy_pass http://127.0.0.1:3000/$1;
        ...
    }