Online purchase declined

He There

I recently got my Low Rate Mastercard, my first try with online payment the transaction declined.
I tried number of times with no success (and missed great bargain at Noel Liming sale ) .
The banker issued the card advised to contact the Credit Card Service Line and ask to unblock my card.
It doesn’t make a lot of sense that I need to unblock my card upon activating but I don’t know about that, and the only way finding this out is to not been able to complete an online payment.
Did anyone experience something similar? Worth looking into this issue.