1. Please login into your Bria X web portal and go to Dashboard -> Manage -> Server Settings.
2. Please click on the pencil icon under "Tools" for the SIP account you want to change the settings for. Now click on "Firewall method" option that would be present in the "Edit Team SIP Account" page. Select each option (NONE, Auto/ICE, STUN), one at a time, and click on "Update SIP Account". Now log out and log in to your Bria X client for the changes to download into the client.
3. For STUN option, please enter the domain that must have been provided by your voip provider in "Firewall server" field below Firewall method. You might also have to enter the "Firewall Server Username:" and "Firewall Server Password:", if your voip provider requires it to access their STUN server. Please confirm with them. You can also try CounterPath STUN server stun.counterpath.com and it doesn't require any username and password to access it.
4. You can omit testing the TURN server if your voip provider doesn't support it.
After selecting every option check if your respective issue goes away or not. Please let me know how it goes.
Note: Remember to log out and log in to your Bria X client every time when you make any change on the web portal, for the configuration settings to go through to the client.