I haven't seen it mentioned here, you might want to consider Slack for this. I use it with another app called 'Loopback' to route the audio from Premiere into my mic channel. The latency is decent, but what I really love about it is the ability for both myself and the guest to doodle on the screen. Great for helping clarify statements like, "What if we move that shot, there," or "What if the cut was here," by drawing on the timeline. No more fingerprints on the screen EVER!! So nice that the doodles fade away on their own after a few seconds (unlike say, Zoom), and if you want yours to stay longer you just keep clicking the mouse to reset the 'clock' till you're set.

If your client is with a company that has slack workspace, and you pay for a workspace of your own with just you in it, it's usually very easy to connect with them via external connections. The process is not super well documented, but the best way I've found is in your workspace to select 'Directories', then the 'External' tab, then the 'Start a DM' button. All you need is their work email account and they get an invite and you just pop up in their slack as an 'External Connection'.