The field "PaymentSource" captures information based on if a payment was processed or not.
0 is for non-processed payments.
2 would be for processed payments.
Processed payments would be something that was entered via the "Process Credit Card" button and would have a value of 2 and any payments that were not using this feature would have a value of 0.
If you ever see a payment without a reference field marked as "Print Reach Pay" you can double-check using this field in an Advanced Find in the payment section.