K2 is using PHP's $_SERVER to determine the visitor's IP. If you are getting the same IP for anyone then this probably means that your server is behind a proxy. So what's the IP you are getting?

yeah my host has proxy.

and i solved problem with your helps.

there is solution:

You have to replace "REMOTE_ADDR" / For Windows Hosts "HTTP_CLIENT-IP" - For Linux Host "HTTP_CLIENT_IP"

Thank you Uluc for sharing the solution :)
I really appreciate it.

I got an issue. I can't see extra fields after select category @ frontend itemform. I saw K2_PLEASE_SELECT_A_CATEGORY_FIRST_TO_RETRIEVE_ITS_RELATED_EXTRA_FIELDS warning after that select category but extra fields not showing.

www.kitapedia.net
username: deneme
pass: thankyouguys

after login there is a yellow book icon. click that and you see itemform. how can i solve my problem?

The K2_PLEASE_SELECT_A_CATEGORY_FIRST_TO_RETRIEVE_ITS_RELATED_EXTRA_FIELDS indicates a missing language string.

The quickest way to get rid of it would be a language overrider docs.joomla.org/J3.x:Language_Overrides_in_Joomla

As for the fields that are not appearing, I was not able to locate the form. However this issue is caused by a JS error. Opening the console tab of your browser's developer tools will show you this error.

krikor it's not missing i wrote that because you wont understand in turkish :)

add item form is after login. there is yellow book near social media icons.

Got it. :)
imgur.com/P5Ian6m

The template is throwing these two errors (the middle one is not an actual error). These errors are preventing the form to work properly since the fields are being loaded with JavaScript.

You need to address these JS issues to the template's developer.

it's mine :) i create with artisteer 4

Now I get a "GET kitapedia.net/component/k2/extraFields/10 404 (Not Found)" error.

Something is changing the URL of the extrafields.
Are you using a SEF extension?

yes artio sef