After some reading on the official Google Forums, I've found that users had no luck fixing this solution even after they contacted Google Support and tried all the possible fixes. It appears that DF-RPC-01 is an issue on their end and a LEVEL 3 technician needs to look into it.
However, on your part, simply switch to another network, and make sure it's secure. When buying, check the payment methods and add it again if it's not there since the error is directly related to payment methods.
