If you are trying to add an event and it doesn't show it in your Opus One, please try to verify all steps below:
1) Did you already add the Calendar on your Calendar app first?
I mean here:
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2) Make sure you select your Default Calendar on Opus One
You need to go to your Opus One>Preferences>Calendar>Default Calendar
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3) Make sure your Calendar is not Hide in your Opus One and Calendar App
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4) Verify permission on your Calendar
In order to do that, please go to "system Preferences">Security&Privacy>Calendar
Make sure Opus One is selected.
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