Multi-WAN network issues
Many routers support multi-wan capability to increase available bandwidth or add redundancy. Depending on the type of connection load-balancing performed, you may experience unexpected results such as disconnections or one-way audio. This is due to the public IP address of outbound traffic switching depending on the WAN link used.
If do you have a multi-wan environment in which you wish to make calls through Close.io, make sure you only bind VoIP traffic to a single link. Create a static route for all SIP traffic (TCP or UDP ports 5060-5065) to be sent over one of your WAN interfaces. This will ensure all SIP and RTP traffic is directed over a single WAN.