According to the support :
"You can't request simbrief with the engines running is what I mean to say.
The FCOM says the "CPNY F-Plan request" button should removed when engines are running."
Same here even after 1.0.2 update - in FS2020 - the F-PLN appears after some manipulation (I insert FROM/TO - Flight number - PAX ) and so on
But It would be better to have it directly in the INIT page