Opencart 2.3.0.2 Notification alert issue. on changes made under Extensions >>Extension

I have been working on OC 2.3.0.2 version , i installed a extension for payment gateway wherein i faced a issue while activating the extension it says "Permission Denied!
You do not have permission to access this page, please refer to your system administrator." , and i noticed that the next click of yours no matter where and which link you click in opencart admin portel the moment take your finger up from the mouse , you could see a message with light-green saying
"Success: You have modified PayU account details! " ... here in my case i am working with PayUExtension. Anybody any hint why this happens..? Apparently the message of -"Permission Denied!
You do not have permission to access this page, please refer to your system administrator." should not have come right...? as the changes i made to enable the PayU Extension was successfully saved , however the Success message didn't appeared , but it showed-up on your next click on any of the link inside opencart admin.

Please somebody help here...My opencart version is 2.3.0.2.

You are posting in the v3.x releases section. In addition, since this issue is about an installed extension, contact the extension developer to resolve this issue.