I do not remember if I bought the credit first.

But, you can try to verify your phone first without buying credit, If it does not work, then you can buy credit and try again.
verifying nonoh.net account you have to do the following:
1) download softphone of nonoh.net
2) verify your account with softphone, by making a phone call to anywhere with your home phone, which canbe your land line phone, cell phone, or VOIP phone.
3) setup phone line with your ATA