It sounds a little bit strange but checking out the system error messages customer gets could produce quite interesting results and leads. 

Let me explain how this could be possible: if a customer gets such a message it means s/he wants to do something but we do not allow this action for a valid reason. Some examples of such messages are "insufficient funds, over limit transactions, blocked password, your electric bill is not paid or can not be paid etc.." It is very easy to find out how many clients receive such messages each and every day.

So let's go to more details for "insufficient funds" error message.Who gets this message and why? Probably a customer who would like to perform a money transfer or purchase a financial product. Well.. some of the clients who receive such messages could also be eligible for loan offering for sure and this could be an excellent opportunity to sell the credit product to him/her at the moment of need. Of course, some propensity model work at your CRM, or at least some profiling may give you the clue who can be eligible for such an offer. It works quite well, I can tell you this from 1st hand experience! Not necessarily for online banking only, but also for ATMs and Contact Centers too.

Actually we discovered this by chance, once we experienced a system interruption and we had to check how many clients were influenced. Considering there are millions active users (thanks God only a small percent of them trying to access to the system at the time of the interruption - but even so it was a big number), it was quite tiring and boring task. So adversity triggered the intelligence (!) - and the idea came to our mind, decided to give a try - organized a pilot and amazed with the results.

Most of the time, micro loans would be good and simple products to sell in such occasions.