It does not appear that most of the help is actually reading the problem trying to be solved.  It is a Clients/Customers PO, they give us a Blanket PO for services to come, this is good until all money has been spent or an expiration date.  

My Client says: "here is a PO for 1,000 for hours you bill the me for."  Might be $100 one month and $300 the next month, etc.  but you need to make sure that when you have hit the $1,000 mark (or whatever their PO was for) that you reach out for a new PO (aka preauthorization to get paid) or quit working for them since that is all they have agreed to pay you.

We are all looking for a way to tie that in with our customers account, like a credit limit, and know when you reach that credit limit.

The estimate idea is a good one, except I have to list multiple line items on one invoice, one for each time something is done for that client, so I am not sure how to keep partial billing from the same Estimate line item. (I don't think that is the answer)

On Desktop we can set Customer credit limits, Is that possible online and if so, can it warn us or alert us to the balance left, but actually that would only work for open balances, not for the overall amount billed toward that customer PO.  

Let me knw if anyone has more ideas on problem solving this, it seems like there should be an easier way.

Thank you all!

Melissa