I don't see any of the appointments I have in my agenda in TimesUpp...

There are several issues that can lead to these issues:

1 You have denied permission to TimesUpp to access your agenda. You can fix this by changing the calendars settings in iOS’s privacy settings.

2 The in-app (view) settings for your agenda are set to hidden. You can fix this by navigating to manage calendars in the settings menu.