Sage Sole Trader doesn't let you create or store supplier invoices. You might also know these as bills or purchase invoices. This is by design.
Sole Trader uses cash basis accounting. You record an expense when you pay for it, not when the invoice arrives. So there's nothing to enter until you pay the supplier.
When you've paid a supplier, you can record the money out and keep a copy of their invoice for your records. There are three ways to do this.
If you’ve connected your bank and already imported the payment, choose this option for the quickest result.
For the steps to attach a file, see Add attachments.
Use this option when you haven’t connected your bank or haven’t imported the payment yet.
For the full steps, see Add expenses - money out and Add attachments.
On paid plans, you can scan the supplier's invoice and let Sage create the transaction for you.
For the steps, see Auto create transactions using receipt scan.