I have OS PAY and WELCOME BOX plugins installed.

WELCOME BOX pop-up window can be closed in two ways. By clicking on the welcome window X icon located on the top right corner or by clicking somewhere sideways on the screen.

But when PAY plugin is enabled the welcome pop-up window can't be closed. X icon nor clicking sideways doesnt work and the welcome pop-up window stays permanent on the screen.

This is probably caused by this js error shown in the console:

user.js:288:3

Uncaught ReferenceError: Tipped is not defined
    <anonymous> https://mydomain.com/oc-content/plugins/osclass_pay/js/user.js?v=20200920184359:288
    jQuery 4
        k
        fireWith
        ready
        D
When PAY plugin is disabled this error is not in the console and the WELCOME plugin works normally (the pop-up window can be closed)

in user.js of plugin find:
  Tipped.create('.osp-has-tooltip', { maxWidth: 200, radius: false, behavior: 'hide'});
  Tipped.create('.osp-has-tooltip-left', { maxWidth: 200, radius: false, position: 'topleft', behavior: 'hide'});
  Tipped.create('.osp-has-tooltip-right', { maxWidth: 360, radius: false, position: 'topright', behavior: 'hide'});

replace with:
  if ($.fn.Tipped) {
  Tipped.create('.osp-has-tooltip', { maxWidth: 200, radius: false, behavior: 'hide'});
  Tipped.create('.osp-has-tooltip-left', { maxWidth: 200, radius: false, position: 'topleft', behavior: 'hide'});
  Tipped.create('.osp-has-tooltip-right', { maxWidth: 360, radius: false, position: 'topright', behavior: 'hide'});
  }

I could not test so let me know if works.