I personally had the same issue on my recent Amazon purchase. Having entered the information thrice, my payment was still rejected. However, when I used a Visa credit card from another bank, it was easily accepted.
The reason for this issue is still unclear, but a call from a BDO customer rep suggested than Mastercard may have blocked online payments due to some complaints and issues from questionable transactions. I’m not sure if other banks are also affected.
The workaround for now is BDO’s Virtual Card. That could served as your temporary proxy account number since it has a different account number.
Are you also encountering issues from BDO Mastercard online payments?