How to Create an Invoice Web App Using Google Sheets and Apps Script | B34

Billing that knows what is on the shelf. The product list is built from your stock sheet, and it will not let you sell what you do not have — then the invoice prints and emails itself to the customer.

Stock decides what you can sell

Two things happen automatically. A product with zero stock disappears from the dropdown, because offering it is how a sale gets promised and then apologised for. And entering a quantity above what is available raises a toast and pulls the figure back to the stock on hand — type 34 when 32 exist and it becomes 32. Overselling is not a mistake you have to notice; it is one you cannot make.

Tax and discount, your way

Tax is a percentage entered per invoice rather than a fixed rate in the code, so the same build works wherever you are. Discounts are entered as a percentage too. The subtotal, the tax amount, the discount and the total are all shown as they change, so nothing is worked out on a calculator beside the screen.

The customer gets it twice

Submit and two things happen: a printable slip is available with your shop name, the customer's details, every line and the total — and the invoice is emailed to the customer's address with the same breakdown plus an additional information line for your return policy or terms.

The sales record

Every sale lands in the sales sheet with its date and time, the customer's details, and each item with the quantity and the price it sold at. Because the price is recorded as sold rather than looked up later, you can open a customer's history and see exactly what they paid at the time — even if the product's price has changed since.