Configuration option against Contract Variation forms: "Allow progress to be claimed per line item".
1. Go to Configure > Document Types >
2. Choose the required variation form.
3. Scroll through right hand pane.
4. When Allow Progress to be Claimed per Line Item is selected,
...
a progress claim can be submitted with an amount or percentage against line items.
5. If there is a Parent Row only Child line items can have an amount or percentage claimed against it.