yea most sites period no matter what it is only accept  Visa or Mastercard .. no american express or discover.. i ran into that problem when somebody gave me an American Express gift card and couldnt find a place to use it online ( i use cash in the real world but i use my card online all the time)  


the solution to your problem is to just do what i do.. theres a site i use that puts me through a bunch of bull if i was to use my normal mastercard so i just go to the grocery store and buy a temporary VISA gift card and use that online.. (temporary means one time you cant reload money on to the card its just used for the one time you need to deposit some money like online)

ALL the VISA gift cards are in the gift card section of your grocery store or above the candy in the checkout aisles..  

just buy one of those they come in $25 $50 or $100 amounts with a small fee like $3-$5 .. and then just go online (to the address they give on the card package ) and activate it ..  all you do is put the number on the card that you bought and the security code on the back of the card in the box  on the website and then once your in you just put in the same first and last name and address you signed up with the online slot website with... and thats it its activated and  ready to use  ANYWHERE online.. just put the card number in just like you would with any other regular Visa credit card or debit card and your money is ready to use at the online slots...


(the card works at gambling sites so you dont have to worry about the info the guy above posted)