nginx Prestashop nginx configuration : all url with /index/ redirect to index.php

[Pierre Mooood]

nGinx : 1.14.2
PHP : 7.3.27
Linux Debian 10
Prestashop version 1.7.7.3

Hello,
I've been trying to find the right nGinx configuration for 2 weeks for my prestashop...
i have a vps server which i configured myself and i think i forgot or did something wrong.

So, my problem is : 

I would like to configure my server to install several prestashops.
I currently have 2 prestashop installed on it that work.
However, every time a url has /index/, I am redirected to the index.php of my server.

For example, when you click on "orders" in back-office : 
http://mysite/my-theme/admin/index.php/sell/orders/?_token=35PTKIihVJnbmnfi_jzLoa2c5dC2Lb3yvWn_V5hR5Ow

Thanks for your help !