Please follow the steps mentioned below to auto-fill the last charged price for a customer when creating an invoice:
Step 1: Go to Settings
Step 2: Go to Preferences >> Document >> Sales >> Enable Use Recently Charged Prices option >> Click on Save changes
Step 3: Go to Sales >> Invoices >> Click on +Create Invoice
Step 4: Select the desired customer and product >> The previously charges prices will be applied in the invoice as shown below
Please note: This is available only in the web/desktop version.