The League Pro Subscription bonus does not increase how many League Points you earn from a single spin. It is a flat % bonus that increases the sum total of your League Points. This means if you purchase it mid-season, it applies to Points earned earlier in the Season as well!

To see the effect of this, you can go to your member page in your League and tap on the League Pro card by your name.

You will get a pop-up showing how many Points you've earned from machines, how many points the League Pro +% is adding, and your current total League Points for the week

The % bonus and League Points it adds go away if your Pro Subscription expires.