From VoIP.ms Wiki
The Two-step verification system adds an extra layer of security to your VoIP.ms account. Once activated, the next time you will log in into your portal, you will be prompted to a second verification step which consists of a six-digit code which you will receive on your e-mail. When you enter your code, you may also choose not to ask again for a specific browser, this simply means that you will not be prompted to a second verification step again when you sign in from this very specific browser. However, if you sign in from any other device or browser, you will be prompted to a second verification step.
To enable the two-step verification, log in to your customer portal and from the Main Menu go to Account Settings > Security Tab.
Make sure to click on the checkbox and hit the apply button to save the changes.