When trying to either enter your host's waiting room, or to start a session on an iPad or iPhone, you see this message: Safari cannot open the page because the address is invalid.
Safari throws this error when it cannot find the protocol for launching an application; this happens when a program (in this case, Zoom or VSee) is not installed. You'll need to install Zoom or VSee.
To see which one you'll need to install for your meeting, check which Install button appears in the lower left-hand corner of your waiting room page. (This is the page that has the "Enter Waiting Room" button on it.)
The other possibility is clicking "no" when Safari asks if you want to open the page in "zoom" or "vsee". If so, refresh the page and click "open" on the prompt to try launching again.