It's common for iPhone users to have their privacy settings set as to deny any access to the microphone, camera and location in Safari. In that case, there is a prompt to change those settings, but if that's not clear enough, here is how you can instruct your customers to enable access:
1. Go to Settings. Scroll down and click on Safari.
2. Scroll down to the bottom.
3. Select Camera and Allow.
4. Select Microphone and Allow.
5. Select Location and Allow.
Finally, return back to the link that was sent to connect to the Visual Support session