Oh man. Payment provider data in mongo... even if by now MongoDB doesnt lose data... you REALLY want your ledger or OLTP to be in a relational, transactional database.
This is the tip of the iceberg when it comes to MongoDB's use cases in Financial services. These organisations REALLY use MongoDB for financial data and they are all public references. Relational databases are great for financial data and so is MongoDB.
Don't know what they use now or if they still use it.