How do i create a costume popunder for my site ?

i would like to make my own costume popunder, work similarly to other popunder ad networks like Adsterra but it will have to redirect to a particular URL of my choice.
is there a way i can archive this?

To create a costume popunder for your site, you will need to create a JavaScript script that will open a new window with your desired URL when a visitor visits your site. Once you have the script, you can then add it to your site's code.