We have an ASP.NET web app. want user to enter amount, choose SQUARE credit card link … that amount goes with it …user enters details …page returns to our APP, with the amout that was actually on SQUARE page (in case user changed it). Any examples on how to achieve this ? Thanks
Currently with Square the Checkout API will allow you to set an amount and direct your customer to a Square hosted page. On this page they will enter their card information and when the payment is complete it will redirect them to your configured redirect_url. Feel free to use our example on Git Hub.
Otherwise you can use the Web Payments SDK. With Square Web Payments SDK it provides a secure buyer payment card entry method along with other secure payment methods and your customer never has to leave your site. We have an example of the Web Payments SDK on Git Hub as well. 
Thank you Bryan - really appreciate the pointers