Why is my nginx server dropping post request bodies?

My nginx server has recently started losing the data sent in post requests. I have read that this is due to redirects, mostly from http to https and vice versa. The solutions I have found involve returning a 308 (permanent redirect) instead to preserve post data. To test this, I created a simple php script that just vardumps $_GET and $_POST. However this has not solved the issue of the post requests dropping completely. below is my nginx server config:

server {
    listen 443 ssl;
    listen [::]:443 ssl;
    ssl_certifcate /path/to/ssl/certificate.crt;
    ssl_certificate_key /path/to/cert/key.key;
    ssl_stapling on;
    ssl_stapling_verify on;
    root /path/to/files;
    index index.html index.php;
    server_name sub.domain.us;
    location / {
        try_files $uri $uri/ =404;
    }
    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
    }
}

server {
    listen 80 default_server;
    listen [::]:80 default_server;
    root /path/to/files;
    index index.html index.php;
    server_name sub.domain.us;
    location / {
        return 308 https://sub.domain.us$request_uri;
    }
}

Any insights into why the request bodies are still dropping would be much appreciated.

source https://stackoverflow.com/questions/75823244/why-is-my-nginx-server-dropping-post-request-bodies