Shift Debit card works for purchases but declined for deposits on global/ignition?

Okay so I have been using my shift debit card for many purchases and getting cash from ATM's and cashback from wal-mart sense i have gotten it. and it is amazing; it works with no issues for these purposes. The question i have is why is it that it works for anything i want except for trying to put money onto a poker site? why is it shift debit card from coinbase gets declined as a deposit option on those online poker sites yet it works for almost everything else in my day-to-day purchases?