Paypal Sandbox transactions are not shown<>
This question already has an answer here:
See my answer in Why is DoExpressCheckoutPayment required for Paypal? In order to use Express Checkout, you must call at least the following API calls: 1. SetExpressCheckout -- to set up the transaction. 2. DoExpressCheckoutPayment -- to finalize the transaction.
If you don't call DoExpressCheckoutPayment on the page specified in SetExpressCheckout's RETURNURL parameter, the transaction is not completed. This is by design to allow for greater flexibility in the checkout flow.
Express Checkout is intended as a drop-in solution in your own checkout process. After Express Checkout redirects you back to your site, you're supposed to show an order confirmation where the buyer can review his/her final order details before initiating a button / link which initiates the final DoExpressCheckoutPayment API call. This is why DoExpressCheckoutPayment is required.
First of all, I'd do a payment from one test account to another using the regular "Send Money" interface and check that the payment shows up, just to rule out the possibility that the PayPal sandbox is acting up.
As for express checkout, not only do you need to do a GetExpressCheckoutDetails after the user is returned to your site, but you'll also need to do DoExpressCheckoutPayment before the payment will show up (as pending or as completed, depending on whether you're doing a Sale or an Authorization. If you don't call DoExpressCheckoutPayment then PayPal assumes your user left your site or otherwise didn't confirm the transaction.
This is my favorite reference for how to do EC: https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/e_howto_api_ECSimpleIntegration