paypal, like other payment services, offers two options for their payment systems.
One is disconnected from the site where the user is redirected to the parent page from the iframe (usually) you clicked on.
Another option is integrated, where your transaction runs carefree on your site so that you never leave the page.
Your first step is to decide which one you want, costs, fees for paying for services that you are ready to handle. If you are big enough to have a trading account.
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