You can enable the ability to apply an invoice to a budget. Go to Business > Settings > Budgets to find these settings.
Firstly enable the feature.
You can choose to either adjust a budget with the invoice that’s created or to create a retrospective purchase order as well. If you enable the workflow step, you will be able to create a new workflow step of “Apply to Budget”.
You also choose to apply this on the creation of the invoice or as part of a workflow.
The latter would require you to place the “Apply to Budget” workflow step in your invoice approval workflow.