The following setup focused on creating a Default payment option on the Buy menu (Now/Later Payment) menu. If your purchase transaction wants the default setup as Later, this can make it easier for you when inputting invoices, you don't need to switch Payment (Now/Later) for each transaction. For detailed setup steps, you can check the following article.
Step 1. Go to Setup, Click More Menu, then Select Module
Step 2. Go to Buy Tab, Set Default Payment, then Click Save
Note:
Switch to later if you want to Later Default Payment
Step 3. Make a Purchase Transaction to View the Result
If this setup has been done according to the method above, it will immediately display the Later option when you make a Pay. So you don't need to change the payment from Now to Later manually.