Basically, it means that you need to wait 30 seconds after your last call before making another. If the issue persists, please log out of the app and ensure that it isn't running in the background. Please follow the link and the 'Close an App' section that is most relevant. https://help.apple.com/iphone/9/#/iph1a1f981ad
To enable screen reader support, press shortcut Ctrl+Alt+Z. To learn about keyboard shortcuts, press shortcut Ctrl+slash.