When you're taking payment in Housecall Pro, the full amount does not need to be accepted at once. You can change the amount that you're collecting on the payment screen.
To do this from the web portal, go to the job's details page and click the 'payment' button.
From this pop-up you can change the amount and choose the payment type. The amount will always default to the full amount due, but you can delete it and choose the amount you would like to mark as paid.
Once you've added the amount you want to bill for, click paid. You will then see the updated balance on the invoice preview as well as just below the 'payment' button.
Remember, can only accept an amount less than or equal to the cost on the invoice!