First thing you need to do is to get a NeuTrafiX Buyer Account
Second thing is you need to allow your FreeSwitch IP inside the NeuTrafiX Buyer portal.
Here is a screenshot of a working configuration between FreeSwitch and NeuTrafiX. The dial plan variable is the seller Tech prefix you need to use, so for example if you want to send the calls to Seller X you will insert Dialplan Variable: 32270#