Method 1:
Edit the file index.php and after line 37 which is global $userpro; add this:
$userpro->validate_license('whatever-license-key-you-want-displayed-here');
No need to do anything else, upon reloading the dashboard it will be activated and nag messages will be gone.
Method 2: Just use below key to activate the plugin
0d9266ab-4233-42ee-b48b-5fc5bfb8ee5f
Method 3
Go to admin-notices.php and add:
update_option('userpro_trial', 1);
So it become like this:
function userpro_admin_notices() { update_option('userpro_trial', 1); if (current_user_can('manage_options') && get_option('userpro_trial') == 0) { userpro_admin_notice( sprintf(__('You are using a trial version of UserPro plugin. If you have purchased the plugin, please enter your purchase code to enable the full version. You can enter your <a href="%s">purchase code here</a>.','userpro'), admin_url() . 'admin.php?page=userpro&tab=licensing'), true); } }