Instant Opt In web link not tagging remaining contact on same computer

Your software
My Mautic version is: 4.02
My PHP version is: 7.4
My Database type and version is: MySQL 8+

Your problem
My problem is: Remaining contacts are not being tagged after clicking opt in web link in email

These errors are showing in the log: none

Steps I have tried to fix the problem: none

There a form set up to send email to the contact with a link to the confirmation page that will assign tag to the contact when clicked. I found it off of a tutorial on “Instant Opt In” without needing to use campaign.

It is working but only thing is that it won’t work on same browser. If someone log in a web mail and click on the link then it will tag that contact but when that contact log out and a different contact log in web mail on his own account then click link, it will not tag the contact at all. Only way to get this contact tagged is to go on mobile phone or a different device where the web browser had not been used by previous contact to sign up for newsletter.

The person who create the instant opt in tutorial suggest using KIOSK mode on the form which I enabled and I did another round of test. It would not tag any new contact on same computer once it tagged the first contact.

I am using an web page that is on our domain not the Mautic landing page since the editor seem not to be playing nice with me .

The code I have on that page

    <img src="<? echo $_GET['email'];?>&tags=BTG">

The link I have in the email to click for confirmation is

Do I to add an email parameter in the link or direct to page link is all I need?