We are new Zoom Phone users.  Things are generally OK but users are complaining that contacts that they enter into the phones are randomly lost.  
Have tried researching the issue and saw a possibly cause could be a blocked port on our firewall  preventing the contacts from syncing with Zoom - but no details on what port to look for.

Any suggestions on how to troubleshoot is greatly appreciated.

Thank you.

You have reached the limit for the number of attendees you can add at this time. Contact <a href="https://support.zoom.us/hc/en-us/articles/201362003" target="_blank">Zoom Support</a> for more information.

I have created 1 webinar, my license is 500 people, I want to invite my clients through system invitation from zoom, Invitation folder -> Manage Attendees -> add CSV file but got the above error, can anyone help me?

I have a new employee who is able to log into Zoom via SSO successfully on both his Mac and iPad. We've done a video call successfully, as well as being able to send him a direct chat message. 

However, he is completely unable to start a new chat with anyone who hasn't sent him a message first. When he selects Chat > More Options > New Chat, and then attempts to enter another employee's name in the "To:" field, only people he has received chats from already show up. None of our other employees show up for him to reach out to.

This is also the case when he navigates to the "Contacts" tab in the main Zoom window, as well as attempting a Search in the master search field. This behavior is happening on BOTH his Mac and iPad, so it's not specific to a device. 

This is causing a major disruption in his workflow, as we use Zoom as our primary method of internal communication. Does anyone have any ideas? What am I missing?

The office manager of our company recently left to pursue other other goals. Now, no one can log into our Zoom account to change any of the email or user settings. I have the login information the office manager used but it will not allow us into the account. If it was a free account it wouldn't be a big deal but we upgraded last fall. Anyone have any suggestions? Thanks!