InvoiceNinja 5 Image files (.png) 404 not found error although they exist on server

My YunoHost server

Hardware: VPS bought online
YunoHost version: 11.11.20
I have access to my server : Through SSH
Are you in a special context or did you perform some particular tweaking on your YunoHost instance ? : no
If your request is related to an app, specify its name and version: invoiceninja5 5.5.113~ynh1

Description of my issue

I setup InvoiceNinja 5 and also made the invoiceninja5 directory accessible to my main yunohost user via SFTP (with this tutorial Give SFTP permission to edit an app | Yunohost Documentation). The problem I am facing is that .png files which are definitely existing on the server in the correct directory (I double-checked) throw a 404 Not found (nginx) error. The strange thing is that .pdf files which are also stored under the /public/storage/.../documents path are shown correctly. So, perhaps this is an nginx conf issue? Can anybody help with this? I want to be able to access my uploaded images in InvoiceNinja.

I looked deeper into this and here is my analysis so far.

Permissions of files:
The directory where the .png files are in has drwxrws---+ permissions and the files themselves have -rw-rwx---+ permissions. Note that also the .pdf files in the same dir which are displayed correctly have the exact same permissions.

Nginx configuration:
I took a look into invoiceninja5.conf under /etc/nginx/conf.d/domain.tld.d where I found the following:

 location ~* \.(?:png|html|ttf|ico|jpg|jpeg|bcmap)$ {
    try_files $uri /var/www/invoiceninja5/public/index.php$request_uri;
    # Optional: Don't log access to other assets
    access_log off;

I’m not too deep into nginx config. Does this look correct considering the .png files are located under /public/storage/…/documents ?

Any advice appreciated! :pray: