I have Pro licence and when I start meeting from browser, I always get dialog "Keep meeting like a pro" and I cannot run meeting with pro licence. When I start meeting from local application, it starts OK.
I am trying it in Win 10 and last version of Edge and also last version of Chrome and in both cases it is same.
We have three Pro accounts and this behavior is same for all accounts.
I am using Windows 10 Pro version 1909, Edge 86.0.622.69, Chrome 86.0.4240.198. In both with the same results. I tried it also on Windows 8 and Edge and it was the same.
It seems like during starting meeting from browser system does not recognize logged user or his licence.
Can you check your online GoToMeeting account to see if a 'Free' license is, or has ever been applied to that Organizer account? Start by checking the Billing section to see if a 'Free' license still exists there, and try to cancel it if so.