AVOXI Call Forward to RC

We are attempting to configure the AVOXI virtual number service to call forward to our RingCentral instance, AVOXI has a VoIP/SIP/Softphone forward option, and we are unclear of the configuration and cant find anyone at RC that can help. They also have an option to just call forward to a number, but the VoIP/SIP/Softphone option is less expensive. has anyone used a third party service like AVOXI to rout numbers to RC?