Money Mistake

I just discovered that I missed paying my water payment this month. It is now 6 days late, which is really too bad because the city really has a steep penalty (like $15). I'm not sure how I messed up. I've been paying my utilities online since January and I was certain that I had scheduled the payment to be processed last week. I was pretty busy last week and didn't check my balance closely. When I looked this morning, my bank balance was more than YNaB said it should be. When I checked the online payment history, I was appalled. I'm not sure what went wrong, but I have a plan to prevent future mistakes:

1. Schedule all my online payments by the 10th of each month, since most of the bills arrive during the 1st week.

2. Double check the bank on the 15th (payday) to make sure everything is in order.