Will clients be able to pay without leaving my website?

Yes, if you’re using the iframe widget.  The iframe widget uses HTTPs and our SSL certificate, so payment information can be securely transmitted from your site.  Unfortunately, this isn’t currently possible with the javascript widget; in that case, clients will be redirected to your landing page (https://yourbusiness.fullslate.com) to enter payment information.

It's also important to note that if you're using Paypal Checkout Express, the payment process will occur on Paypal pages and the client will be directed to your landing page at the end of the payment process.