Updated August 10, 2019
Cloud: Once your cloud instance uses all of its allocated bandwidth, it will begin to accrue overages. Additional bandwidth costs $0.004/GB. Only outgoing public traffic counts toward your usage. Usage resets each month.
SolusVM (Legacy): If your VPS uses all of its bandwidth for the month, it will be automatically suspended. You may buy more bandwidth at that point or ahead of time. Please see the How do I order more bandwidth? article to order more bandwidth.