Possible reasons for card decline:
1. Your system setup is leaking and/or does not match the cardholder.
What do you use antidetect or virtual machine?
2. Dirty IP address. On what sites do you check the cleanliness of your IP address before paying with a card?
3. It is not possible to buy cryptocurrency using the bins of the cards you use because they are included in the stop list.
4. The card is invalid or there is not enough balance on it. How do you check the validity of the card?
"CAUSES OF DECLINE OF A VALID CREDIT CARD":