When a new invoice is raised for a proposal, the payment collection date will be chosen based on your payment terms settings in Settings → Payment Gateway.
However, if you'd like to alter the default date, you can do so by following these steps below depending on whether the invoice has been raised yet.
Invoice has not been raised
If the invoice has not been raised yet, you can simply edit the billing item in a clients Billing Schedule tab and change the date to be a future date of your choice.
Invoice has been raised already
If the invoice has been raised already but the payment collection hasn't started. Click into a clients Invoices & Payments tab and click into the specific invoice.
If the collection hasn't started yet, click Schedule payment and select when you would like to collect for this payment.
If the collection is already scheduled, click on the 3 dots and then click Reschedule. Then, select the new date that you would like the collection to happen on.