Delete the incorrectly registered purchases, and link the invoices to the existing contract instead. Installments should not be registered as separate purchases, because that doubles the cost.
How to clean up
Go to Purchasing in the menu.
Find the lines registered as installments, for example "Installment 01".
If invoices have been linked to these lines, move the link to the main contract.
Tick the lines to remove in the checkboxes on the left. You can select several at once.
Choose Delete in the menu next to the checkbox in the table header (for example "2 Selected").
Check that the final forecast on the production code is now correct.
Good to know
A contract is registered once with the full contract value. Each installment arrives as an invoice that is linked to the contract.
If you want to plan when the installments arrive, use the payment plan on the contract.

