Configuring NGINX to emulate API in PHP

Question

I am trying to emulate an API path to reroute to a PHP script. I'm trying the following configuration (found here), but receiving a 404.

location ~ ^/api/v1/(.*)/?$ {
    try_files $uri $uri/ /v1/index.php?req=$1&$args;
}

I am expecting any request that comes in through .com/api/v1/user/alert/123 to be received by the script in /v1/index.php and can be captured as a $_SERVER['REQUEST_URI'] path (e.g. /user/alert/123).

Any suggestions?