Tarjeta promocional

I just went to use my 200.00 promotional debit card at a store and it asked for my PIN number. I looked online as to how to set pin and it states to look on the back of the card for the website to go to. But I am unable to see the back of the virtual card. Has anyone had this issue? Do I use my PIN from my T Mobile account? ¡Gracias por tu ayuda!