WebDAV "413 Request Entity Too Large"

I have turn on the WebDav in services, use HTTPS protocol. Now, I can access to the webdav folder normally, also can upload and download files.
But, when I upload a file which size larger than 1000m, the webdav client will respone the error of “413 Request Entity Too Large”.
I have try to modify the “client_max_body_size” from 1000m to 10G in “/etc/nginx/nginx.conf”, but it didn’t work.
Even I restarted the truenas system, the “client_max_body_size” parameter in the conf file will changed back to 1000m.

Can anyone give me some help? Thanks!