Getting 413 Request Entity Too Large on Plesk hosted website

Once in a while, I have some issues on Plesk when nginx is enabled. Every post request returns a 413 Request Entity Too Large response, preventing the web applications to work properly.

What is happening

For every POST request made to the web application, a 413 Request Entity Too Large response is returned, even when the request body is empty or very low:

413 Request Entity Too Large
nginx

In the domain Apache & nginx Settings, the Maximum allowed HTTP request body size is set to a high value (much higher than the request size) :

Requests and errors are not showing up in the domain logs :

Why it is happening

I couldn't figure it clearly, but it is clearly lin to the nginx configuration. Since the requests don't appear in the domain log, I supposed that a global server configuration is overriding the domain settings, preventing the request to even reach the domain.

How to solve it

I could get a workaround by adding a global client_max_body_size value in a global nginx setting file.

However, this will override any local per domain settings made in Plesk in the Apache & nginx Settings section.

Step 1: edit the nginx default file

Connect by SSH to the server and enter the following command to edit the nginx default file:

nano /etc/nginx/nginx.conf

Add the following line to the http section :

http {
    [...]
    client_max_body_size 512m;
}

This will allow a post size of 512MB server-wide.

Step 2: restart the server

systemctl reload nginx