KA REST API - problem with Authentication

Summary:

Trying to use Postman for testing API, but when I try to authenticate API User it returns error.

If I generate the auth token via PHP Okcs model (makeApiRequest method), than copy the token to Postman and try to get some articles it works (the siteName should be correct). My problem is only with authentication in Postman.

Content (required):

I've got this error (response):

{"error" : { "title" : "An application error has occurred. Root Cause: There was a problem loading tenant data from the Database: JDBC Connection Provider Error: Unable to get data source.", "errorCode" : "OK-GEN0003", "type" : "APPLICATION" }, "errorDetails" : [ ] }

Same as this article, but the siteName is required everywhere (not only in authentication), so this param should be correct in my case.