I paid for the PRO version but it's not working

Sounds like it's not activated.
If you click on the account icon top right, you should be prompted for an e-mail address.
Make absolutely sure that it's the same one you used when you bought the Pro version.
You should get a message sent to that address with a link to click on to activate the program.

No it's not that...I tried multiple times.

It seems to be working now....I'm guessing it was a delay in the authorisation

Good to hear, I hope it now keeps working for you!

It's a great program (when it works).

Cheers, Dave.