You might find it beneficial to split payments into two parts when providing services -- an upfront payment at the beginning of the project and a final payment at the end.
You could, for example, bill 50% upon agreement acceptance and the rest after the job has been completed.
Here's how you can set it up:
Create two different services in the same proposal
The first service can be called "Service X - Upfront Payment" and you would set its amount, for example, to be 50% of the total cost of the service.
Set it to be billed one-time, automatically, on acceptance.
The second service would be called "Service X - Final Payment".
Set it to be billed manually so that you can decide when it gets billed.
When you're ready, go to the Billing Hub and bill the service using the Billing Control button.