If you want to automatically request payment from your client right after they accept your proposal, there's an easy way to set this up.
How to require an a deposit when a proposal is accepted
Right inside your proposal editor, you can enable the feature to "Require a deposit"
What your clients will see
Once this is set, your client will be able to see a note stating how much of your proposal will be required to be paid upon acceptance.
Then when your client accepts the proposal, they will be prompted with a payment modal including the payment methods you've enabled.
Which invoices will be created?
Invoice for the deposit
At this point, the underlying invoice (for $1,200 in this example) will be created inside of your account as well as being marked as "Sent".
If, for some reason, your client fails to complete their payment here, you can always send a reminder for the invoice itself separately.
Invoice for the remaining amount
Only after your deposit invoice is paid will the invoice for the remaining amount will be created.