I just installed SS 2.4.4 and the payment and payment-test modules. I see the products but when I go buy, enter my details and then click 'proceed to pay' I just get a blank page with /payments/ObjectForm URL. I can't find any errors in my logs.
I had this problem also. Adding the following details to the mysite/_config.php made this work.
Hope this helps.
// Define which payment methods your site uses.
'DPSPayment' => 'Credit card (DPS)'
//setup test environment