Unclear responsibilities lead to problems and confusion. How to break the responsible person?

I don't know much about the specific invoice type. I have some suggestions to see if I can help you. Please forgive me if I am joking.

Can you count the types of invoices by department, such as department A and department B? Or invoice matters, such as travel or procurement; Or simply define the invoice number (even or odd, I'm not sure); Or monthly, you do 1, 3, 5 and another 2, 4, 6 and so on. In short, according to your previous statistics, the workload of two people is as equal as possible. Then make a rule that everyone is responsible for different things, and then make it public (email or you can indicate in your own seal and signature that you can find others in that case).

Set up a work ledger, write down the name of a manager and the date of processing, put it on the * * * sharing table or the public * * * group, and send it once a month to let them confirm whether their invoices have been received, if there are any problems, and who the manager is, so as to draw a clear line (not to be dumped).

Explain directly to the immediate leadership and let the leadership find a way.

The above is for reference only. Please forgive me if there is anything wrong.