Make sure when setting up a Zoom meeting that you are using this Zoom Add-In
Click the + to add a meeting, it may ask you to login, so login with your zoom credentials. You can also modify any settings that you may need by click on the Settings button.
Also, if you need to add other numbers for other countries to dial in, you can find them in theses settings under the Audio section.
Then just add what ever countries you need.
Then hit Save and Continue and then Update.
If you are supporting other people's mailboxes/zoom accounts, you will find a drop down box in the Settings that allows you to pick who's Zoom meeting it is for. Make sure you go into the Settings first, and select who it is for, then select Add meeting.