Creator of FlyingPress here, Gijo Varghese.
Most of you might start seeing the message
"FlyingPress: Pls enter a valid license key".
Here is why: We do many optimizations from our servers (Optimizer Engine), like generating critical css, used css etc. Till a few days ago, we were not validating license keys at our Optimizer Engine. But we noticed that a majority of the people are using nulled/cracked versions of FlyingPress. So we're now validating license keys at our servers.
Why you can't bypass this: Usually, people who make nulled/cracked versions modify the license checking PHP code and distribute the code. Since FlyingPress optimize pages from our servers, whatever you do in the PHP code, we don't optimize those pages if the license is not valid. Even if you remove that alert somehow, you will not get the advantages of FlyingPress.
I know this is disappointing to many of you. But consider the time and effort we put into building this. Also, our servers cost money.
If you would like to continue using FlyingPress, get updates, new features, premium support, etc., consider buying the plugin from the official website:
https://flying-press.com.