Let us assume that there is a task with an estimated invoicing, which is what you have already invoiced + what you still expect to invoice.
They have already invoiced for DKK 5,249,023 and the remaining balance on the task is DKK 7,335,652. If you add the two numbers together, you get 12,584,675, - as it will also appear in the budget.
How can it be that the total amount is not equal to the total fixed price of the assignment? It may be that extra has been invoiced on the case per intention - it's quite natural. But if you experience it as an error, it is probably because you have not written down the task at the same rate as you have invoiced it. When you press "Invoice now" on a task, you can see how much the task is written down in the lower right corner (illustrated below). An invoice is then formed.
If you subsequently adjust on this invoice, then it does not affect the write-down of the task, and then the two numbers can come out of sync. Likewise, if you make an invoice from scratch and attribute it back to the task, it does not affect the write-down of the task.
We have a project A with a fixed price of DKK 1,000. We now create an invoice of DKK 400, which reduces the balance of the assignment to DKK 600.
If we now make an extra invoice of DKK 300, which we attribute to project A, then this does not automatically write down the project. It could be overtime.
The calculation then is that we have invoiced DKK 700, and the balance is DKK 600. I.e. the expected invoicing is a total of DKK 1,300 compared to the DKK 1,000 we started with.