Make sure you have created the Voice account and set the routing groups by following this article.
To apply the routing group as a Buyer of Voice Service, please follow the following steps:
1. Checking the Technical Prefix on the Routing Groups menu by going to Login as a Buyer > Routing > Routing Groups > on the Prefix column.
2. Send your voice traffic by using the Technical Prefix from your platform to NeuTrafiX. By sending the voice traffic using the Technical Prefix, your voice traffic on that account will follow the Routing Groups' routing arrangement for all destination.
You can update your Routing Groups anytime you want, and it will be applied immediately.