[Solved] When I activate Plugin, it causes issues on my site

@okereke-divine,

I may suggest you install and activate the Query Monitor plugin and check the issues you get. 

Okay. I have just activated the plugin. But I can't really understand what they are saying as the errors.

Also, please explain how this is supposed to solve the issue I have with wp-discuz plugin

UPDATE: 

I just wanted to provide more details:

When I try the "Approve & reply" it won't go through. It will just approve the post and show error message saying critical error on website

If the issue is not from your plugin, then when I deactivate the discuz plugin, I should still face the exact problem. But that is not the case. When I deactivate the plugin, everything works fine.

You have been super helpful, but leaving this case here is not soo good. The google search results are not comprehensible and overwhelming. Please help further

This is a reply from Darshana (WP SMTP Support Staff) on Similar Issue:

Also, our plugin does not require the SMTP class/file if it already exists. Usually, it’s required and initialized by WP core, but some plugins are doing it manually without checking for the class existence before doing so and that is why you’re getting this error.

From the above, please don't think your plugin is requesting the PHPMailer class without checking for the class existence?

I am just lost, please help.

Thanks for the suggestion.

I contacted the plugin and they suggested I install a wp smtp plugin which I did and the issue was fixed.

Thanks once again.