If you are trying to connect to a Telehealth Visit or Event from work, a school, government, or religious organization, you may run into a Firewall issue. There are steps you can take to identify if you are behind a Firewall.
If have a network Firewall enabled, you may see a black video screen or a "Connection Can't Be Established" warning or you may drop connection regularly (like every 10 seconds). 
What can you do?
If possible, please contact your IT department and have them open the necessary Ports (see below).
Minimum Requirement: Assumed by default is that TCP ports 80 and 443 are open. Some firewall rules only allow for TCP traffic over port 443, make sure that all traffic can pass over this port. If you continue to experience issues, you may need to follow the rest of the rules below.
Best Experience: In addition to the minimum requirements being met, we recommend that UDP ports 1025 - 65535 be open.
More info: Our streaming server IP addresses change dynamically and can be any IP address, so you cannot allowlist an IP address range. If you are looking to add our domain to be allowed in your firewall, the easiest thing to do is to allow traffic from all bigmarker.com servers with *.bigmarker.com domain and allow traffic from all myowndoctor.com servers with *.myowndoctor.com domain.
We recommend disabling any anti-virus programs (ex: Kaspersky, Norton, McAfee, AVG, Windows Security Essentials, etc. Be sure to also disable Windows Firewall). Programs like these consume CPU resources, and may block ports needed for a successful webinar experience.
If this does not work, have your IT department email support@bigmarker.com