If you create meetings in Outlook through a browser and attach a OneDrive file, the link to the file will not work in FirstAgenda.
The link is displayed as plain text, not click-bar.
What should I do to see my OneDrive documents in FirstAgenda?
Instead of selecting "Attach as a OneDrive file," choose "Attach as copy".
Once the meeting has been transferred to FirstAgenda, you will be able to access the document.