If I pay, will I get access to more features? Will my app issues go away on payment?

No.

The trial version of the app is exactly the same as the licensed version. The trial will stop after 30 days, the licensed version will continue to run based on your license duration.

IF YOUR TRIAL APP IS NOT WORKING AS EXPECTED, DO NOT PAY FOR A LICENSE. THE PROBLEM  WILL NOT GO AWAY WHEN YOU PURCHASE.