Cannot get user by login via REST API

Hi.

I need to get some user properties inside SharePoint Workflow. For this purpose I decided to use HttpSend activity and REST API.

On development server I didn't have any problem, but on test server I can't get most of the users (actually, I can only get one of them - mine, which is admin there).

Initially I used such request:

http://localhost/_api/web/siteusers/getbyloginname('domain/username')

Then I tested another request:

http://localhost/_api/web/siteusers(@v)?@v='domain\username'

In both cases I get such error response:

User cannot be found

But users actually exist on site, because if I call

http://localhost/_api/web/siteusers/