Sometimes, and frequently enough to warrant this comment, the Financial Manager payment system does not work at the exact moment you are submitting an issue fee payment.
Unfortunately, the system often goes down temporarily and without notice (so the user has no idea that the system is not working) or there is some glitch with the browser being used such that the end result is that the payment system does not work.
When this occurs, it happens only after you press submit in EFS-Web and, as such, the PTOL85B form is submitted to the USPTO. However, if you attempt to fix this by trying again, waiting until the system comes back up, changing browsers, or whatever happens to work for you, you will find that you cannot do an issue fee submission without the PTOL85B form. This forces you to re-upload and re-submit the form (placing two forms in IFW).
It would be nice if you could submit the issue fee payment on its own, or be allowed to if the system recognizes that the form has already been submitted (by virtue of document description of a document in the IFW, for example), or by reference to the earlier form submission (which would require a change in the system that i will submit more generally in a separate idea).