Thank you all for your replies,
The problem is solved, thanks this email reply below: 😎
“Are you on Windows? If so, make sure you have installed the font for all users. Right-click the font name in Window Explorer and choose Install for all users. Oxygen seems to run under the administrator user.
We just struggled with this same issue when getting a new writer up and running on Windows (I’m on Mac)”
I’m on Windows, so what I did was download the font again and right click “Install for all users”