Our goal at Sincerely is to create an unsurpassed mobile ordering experience. We realize that entering your credit card using that tiny keyboard can be a pain, and that for some apps, in-app purchasing is a quick way of paying the merchant for services.
However, Apple and Google currently prohibit in-app payments for physical goods like postcards. We are simply disallowed from integrating with their respective In-App Payments Program at this time.
If you'd like, you can enter your credit card online using your computer at sincerely.com and it will be saved for future use on your mobile device.
With that in mind, we do implement PayPal's secure tokenization technology so that you only need to enter your credit card the first time you place an order. This is a completely secure industry-leading method of collecting payments which does not store the credit card anywhere on your phone or in on our servers - we simply reference your paypal transaction when you wish to order again (you can read more about secure tokenization here).