403 Error on submitting form

Hello
I have this problem
403 Error on submitting form

"Forbidden
You don't have permission to access /admin.php on this server."

CMS: Datalife
url:/admin.php?mod=addnews&action=addnews

Probably mod security. Try disabling it.

I had a similiar problem, in my case, the images was not loaded with forbidden message in the web developer console.

I tried many solutions suggested here, check folder and files permission and disable mod security and all that but failed.

In the end i select the webserver without nginx and varnish cache and it was resolved.