If shop page has proper connection with advertiser, you will see "Go to shop" button on page. If user is logged in, he will see direct link to shop (with your tracking link). If user is not logged, he will be redirected to register page.
You can change color of button
Custom Registration/Login modals
We recommend to ask developers of theme which you use about Registration/Login modals. Many themes have inner registration systems which you can use.
For this, we added two fields in General settings:
Place here URL to your custom register page. This URL will be used if non logged user clicks on button from Advertiser's page. You can place here regular WordPress login link "site.com/wp-login.php" Also, we recommend to install Buddypress on site for User profiles. Then, you can use here link "site.com/register/" which goes to register page of Buddypress.
Go to shop Button Class
You can add custom class for buttons. Some themes have special class which triggers login modal and you can use this class here.
If you use Rehub theme, you don't need to place here anything because theme already has proper classes for buttons. Just enable login popup in Theme option -> User option.