I am using simple form submit to paypal sandbox url 'https://www.sandbox.paypal.com/au/cgi-bin/webscr'.
<input type="hidden" name="amount" value=11>
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="no_shipping" value="1">
<input type="hidden" name="business" value='[email protected]'>
<input type="hidden" name="item_name" value="audio">
<input type="hidden" name="currency_code" value=USD>
<input type="hidden" name="UseSandbox" value="true">
<input type="hidden" name="return" value=returnURL/">
<input type="hidden" name="cancel_return" value=cancel_url/">
<input type="image" align='centre' src="http://www.paypal.com/en_AU/i/btn/x-click-but01.gif" name="submit" alt="Make payments with PayPal - it's fast, free and secure!">
If I am already logged into my sandbox account, everything works fine ,I am redirected to payment page with my merchants test store showing the amount and right side showing payment alternatives. But if i logout from sandbox and then make a payment through the payment page it redirects to login to sandbox paypal..When the buyer buys the item why would he require to login to sandbox. Why cant get direct access to sellers test store.