Default GoSMS Pro Users

I recently purchased the GS4 and I see that GoSMS is now a paid app. It says $5.00 for the pro version. My questions is as it odesn't say. Is it a one time charge of $5.00 or $5.00 annually? I tweeted them but nobody has replied.

Samsung Galaxy S 4 - Current
iPhone 5- Sold
Samsung Galaxy S II (SGH-I777) - Sold
HTC Inspire - returned
iPhone 4S - Sold