Outbound calls with Realtime

I’m trying to make some outbound calls in my Asterisk working in Realtime. When I define “register” sip in sip.conf file like this:

[provider] nat=yes username=login fromuser=login host=5060 type=peer secret=pass context=my_cont host=ip_address fromdomain=sip.itc.provider.com
Everything works fine.
But if I add the same sip to my MySQL database (of course after removing it from sip.conf) I get this error when trying to make outbound call:
Failed to authenticate on INVITE to “xxx” sip:login@sip.itc.provider.com;tag=as22925821’

EDIT: Sorry, it was suppose to be in Asterisk Support, not AsteriskNOW Support. Could anyone move it there?