We’re indies just like y’all. You’ve purchased the engine and can use it for commercial purposes with 0% royalties. The standard version is a one time purchase and the Pro version is a yearly subscription. Regardless of which you choose, you have to write to use the version of the engine you’ve purchased (the subscription is for receiving updates/newer versions).
We’ll put that in a EULA.txt file.
But the bottom line: we’re not trying to screw you over and want you to succeed as an indie.
You should only use the engine if you believe the statement above.